Make uploadlimit an object that stores upload limits for avatars, banners, backgrounds, general content

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.

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()`.

Emoji were broken due to `Pleroma.Formatter` not knowing about the
auto-shortcode emoji. This moves that logic from
`Pleroma.Web.TwitterAPI.UtilController` to `Pleroma.Formatter`.

Additionally, it's now possible to specify multiple shortcode globs, and
the default globs were changed to `["/emoji/custom/**/*.png"]`, since
that's in the .gitignore and the files there would have to be shortcode
emoji anyway.

Also, a bit of formatting, and the glob includes an "/emoji/" prefix to
make it more intuitive to users

This reverts commit b259b4e4.

This reverts commit 47e8c8db.

Mistakes were made.