add account deletion

Ref T319

Previously, it would show a 500. This also logs the real reason if it's
not a "not found" error

Ref T319

Ref T319

Send out ActivityPub mentions

Closes T627

Ref T627

from /mention:

Ref T627

This notifies the user that the remote user doesn't exist, instead of
showing a blank page.

Ref T627

by making them absolute, not relative.

- Export the func
- Remove commented-out code
- Use log, not fmt for debug messages
- Remove named return parameters
- Use standard var naming schemes
- Fix spacing in queries and remove unnecessary chars

Fix memory leak

Switch to a maintained fork of XGO

A minor Drafts page fix + improvement

Add Cache-Control headers on AP endpoints

Closes T693

Fix date format in `datetime` attribute

Previously, the date format in this attribute for posts was invalid.
This caused local date rendering to fail in Firefox. This fixes that.

Closes #253

show timestamps in local date/locale

Posts without an explicit title render the date as the post header in
lists of posts (like on the blog index and tag pages). This updates
localdate.js to properly adjust those dates, too.

update upgrade script for recent changes

This gets rid of the gorilla/context dependency, which might have been
causing a memory leak.

We noticed some serious memory leakage on Write.as that seemed to point
to this library. One heap snapshot:

      flat  flat%   sum%        cum   cum%
  259.13MB 30.41% 30.41%   268.13MB 31.46%  net/textproto.(*Reader).ReadMIMEHeader
  105.71MB 12.40% 42.81%   105.71MB 12.40%  github.com/gorilla/context.Set
   78.53MB  9.21% 52.03%   125.53MB 14.73%  github.com/gorilla/sessions.(*Registry).Get
   55.51MB  6.51% 58.54%    82.52MB  9.68%  net/http.(*Request).WithContext
   38.01MB  4.46% 63.00%    38.01MB  4.46%  github.com/gorilla/mux.extractVars
      35MB  4.11% 67.11%       53MB  6.22%  context.WithCancel
   34.50MB  4.05% 71.16%    34.50MB  4.05%  context.WithValue
      27MB  3.17% 74.32%       27MB  3.17%  net/http.cloneURL
      26MB  3.05% 77.38%       26MB  3.05%  github.com/gorilla/sessions.NewSession
      18MB  2.11% 79.49%       18MB  2.11%  context.(*cancelCtx).Done
   16.50MB  1.94% 81.42%    16.50MB  1.94%  syscall.anyToSockaddr
      14MB  1.64% 83.07%       47MB  5.52%  github.com/gorilla/sessions.(*CookieStore).New
   13.50MB  1.58% 84.65%    51.51MB  6.04%  github.com/gorilla/mux.(*Route).Match
   11.67MB  1.37% 86.02%    13.21MB  1.55%  regexp.(*Regexp).replaceAll
    9.72MB  1.14% 87.16%    22.94MB  2.69%  regexp.(*Regexp).ReplaceAllString
    9.50MB  1.11% 88.28%   115.21MB 13.52%  github.com/gorilla/sessions.GetRegistry

With the help of these articles, we tracked it down to this dependency,
and upgraded the library, which seems to have completely fixed the issue
so far:

https://rover.rocks/golang-memory-leak/
https://medium.com/@walterwu_22843/golang-memory-leak-while-handling-huge-amount-of-http-request-35cc970cb75e

This should fix #133

Require authenticated user for editor access

Previously, we'd show the raw HTML entities in the summaries of Draft
posts, instead of rendering them. This fixes that.

changes accounted for
- the tar directory structure had changed to use a subdirectory
- there are now multiple linux targets released

bugs
- the service must be stopped before replacing the binary
- migrations were not being run during an upgrade

Previously, anyone could access the editor even if they weren't logged
in. They couldn't do much in that case (publishing would fail), but it
could potentially cause some confusion.

Now, users will be sent to the login page, and then redirected back to
the editor once successfully logged in.

OAuth signup form tweaks

Resolves T715

This removes a bit of friction.

Ref T715 T712

This makes it possible to complete OAuth signup without creating a
password on the WriteFreely instance.

A user can then add a password to their account through their Account
Settings page without any admin action (all of this logic is already in
place).

Ref T715 T712

This uses the given username as the Display Name / Collection Title if a
user doesn't give one -- as might happen when authenticating with
Write.as.

Ref T712

Ref T712

"alias" is the name of a different collection field, so this renames the
variable internally to make things clearer.

Having a `Username` field populated in the page data tells the base
template to display navigation that only a logged in user should see. So
this renames the field to `LoginUsername`, similar to our login.tmpl
page.

Ref T712

This checks the user's inputted username as they type it, and prevents
form submission if the name is taken.

Ref T712

All usernames should be lowercase, so this generates any username suffix
(in cases of collision) with only lowercase letters. It also removes
vowels to prevent bad 5-letter words from forming.

Ref T712

add basic text file imports

Resolves T609