Add default robots.txt that allows bots access to all paths.
Add mix task to generate robots.txt taht allows bots access to no paths.
Document custom emojis, MRF and static_dir
static_dir documentation includes docs for the robots.txt Mix task.

See: https://git.pleroma.social/pleroma/mastofe/tags/bundle-2019-03-07

[ci skip]

Fixed `scopes` of apps / authorizations / tokens from apps initially created with space-delimited `scope`.

Make it part of the info thing (and do a migration to ensure it's there)

[#468] User UI for OAuth permissions restriction. Standardized storage format for `scopes` fields, updated usages.

See: https://git.pleroma.social/pleroma/mastofe/tags/bundle-2019-02-10

[ci skip]

Also makes the index a lot smoler.

This reverts merge request !733

This reverts merge request !682

Fixes #552