Preferred usernames, banners and icons. (#1055)

* Re-organizing federation tests. #746 #1040

* Adding federation support for user bios. Fixes #992

* Adding icons, banners, and preferred usernames.

- Added optional community icons, and community banners.
- Added user banners.
- Added Site icon and banner, with custom favicon.
- Set up preferred usernames. Fixes #1017
- Added an additional post sort: Active
  - Hot rank now uses the published time.
  - Active uses the most recent comment time, and is default.
- DB Migration was required to add all these fields to the views.
- Added transfercommunity helper function.
- Removed title column from communities page.
- Abstracted an image-upload-form.tsx, and a banner-icon-header.tsx
- Fixes #899

* Some navbar fixes.

* Fixing css

* Some fixes.

- Showing correct user icon and banner after save without page reload.
- Abstracting diesel update overwrite.
- Adding some docs.

* Adding @ when a user doesn't have a preferred username.