* Add REST API for creating an account

The method is available to apps with a token obtained via the client
credentials grant. It creates a user and account records, as well as
an access token for the app that initiated the request. The user is
unconfirmed, and an e-mail is sent as usual.

The method returns the access token, which the app should save for
later. The REST API is not available to users with unconfirmed
accounts, so the app must be smart to wait for the user to click a
link in their e-mail inbox.

The method is rate-limited by IP to 5 requests per 30 minutes.

* Redirect users back to app from confirmation if they were created with an app

* Add tests

* Return 403 on the method if registrations are not open

* Require agreement param to be true in the API when creating an account

* Compensate for scrollbar disappearing when media modal visible

Make auth pages backgrounds lighter

* Fix typo

* Cas authentication feature

* Config

* Remove class_eval + Omniauth initializer

* Codeclimate review

* Codeclimate review 2

* Codeclimate review 3

* Remove uid/email reconciliation

* SAML authentication

* Clean up code

* Improve login form

* Fix code style issues

* Add locales

* Add GET /api/v1/instance/peers API to reveal known domains

* Add GET /api/v1/instance/activity API

* Make new APIs disableable, exclude private statuses from activity stats

* Fix code style issue

* Fix week timestamps

When a new user confirms their e-mail, bootstrap their home timeline
by automatically following a set of accounts. By default, all local
admin accounts (that are unlocked). Can be customized by new admin
setting (comma-separated usernames, local and unlocked only)