add update checks

Closes T572

This adds a new config option that signifies the admin doesn't need to
see deeply technical things, like application resource usage. In the
[app] section, set forest = true to enable this.

Ref T694

This moves app config to a "Settings" page and the application monitor
to a "Monitor" page. It also reworks the admin navigation bar a bit and
adds some instance stats on the dashboard.

Ref T694

update golang.org/x/crypto vendor to use acme v2

Improve resource use for federation

Rename Suspend status to Silence

Ref T661

Ref T661

add silenced warning on invites page

Ref T661

Ref T661

fixes imported post times

Require authenticated user on draft edit routes

Restrict /invite/{code} route to valid chars

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

- /edit
- /meta

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

This adds the `isIgnorableError` method and calls it when error checking
in `GetUserInvite()`, returning "not found" if the rror comes up.

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

Previously, loading something like /invite/fFdblk😄 would return a 500,
due to a mix of collations in MySQL while SELECTing for an invite with
an ID of 'fFdblk😄'. This restricts the route to [a-zA-Z0-9] chars, to
prevent this.

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.