* Fix admin being able to suspend their own instance account

* Add text about the instance's own actor in admin view

* Change instance actor notice from flash message to template

* Do not list local instance actor in account moderation list

* Add account sensitized

* Fix i18n normalize

* Fix description and spec

* Fix spec

* Fix wording

* Add moderation warnings

Replace individual routes for disabling, silencing, and suspending
a user, as well as the report update route, with a unified account
action controller that allows you to select an action (none,
disable, silence, suspend) as well as whether it should generate an
e-mail notification with optional custom text. That notification,
with the optional custom text, is saved as a warning.

Additionally, there are warning presets you can configure to save
time when performing the above.

* Use Account#local_username_and_domain

* Fix markup in admin/accounts/:id table for avatar

* Add admin ability to remove an user's header image

* Add moderator role and add pundit policies for admin actions

* Add rake task for turning user into mod and revoking it again

* Fix handling of unauthorized exception

* Deliver new report e-mails to staff, not just admins

* Add promote/demote to admin UI, hide some actions conditionally

* Fix unused i18n