Refactoring.

This copies Mastodon API behaviour & fixes Mastalab app.

Related to #85

Everything should now be configured at runtime, with the exception of
the `Pleroma.HTML` scrubbers (the scrubbers used can be
changed at runtime, but their configuration is compile-time) because
it's building a module with a macro.

This removes duplication in the login code.

The changes are a bit heavy since the emojis were loaded into module
attributes from filesystem.

This introduces a GenServer using an ETS table to cache in memory the
emojis, and allows a runtime-reload with `Pleroma.Emoji.reload()`.

When we lowercase the search it will succesfully do a case insenstive
match. Now #Linux will match #linux and #LINUX whereas previously it
would only match the exact case.

Better be sure than sorry

lib/pleroma/web/mastodon_api/mastodon_api_controller.ex: Output an error when render(status.json) gives a nil

This reverts commit c1d07da4.

The fake support was superseded by 6e030129 which actually implements the faked filters API.

This change removes the fake support and ensures that the actual implementation is used.