- Add file_name field to `RealmEmoji` model and migration.
- Add emoji upload supporting to Upload backends.
- Add uploaded file processing to emoji views.
- Use emoji source url as based for display url.
- Change emoji form for image uploading.
- Fix back-end tests.
- Fix front-end tests.
- Add tests for emoji uploading.
Fixes#1134
Finishes the refactoring started in c1bbd8d. The goal of the refactoring is
to change the argument to get_realm from a Realm.domain to a
Realm.string_id. The steps were
* Add a new function, get_realm_by_string_id.
* Change all calls to get_realm to use get_realm_by_string_id instead.
* Remove get_realm.
* (This commit) Rename get_realm_by_string_id to get_realm.
Part of a larger migration to remove the Realm.domain field entirely.