Merge branch 'feature/770-add-emoji-tags' into 'develop'

.gitignore

config/config.exs

config/emoji.txt

docs/api/pleroma_api.md

docs/config/custom_emoji.md

lib/pleroma/emoji.ex

lib/pleroma/formatter.ex

lib/pleroma/web/common_api/common_api.ex

lib/pleroma/web/common_api/utils.ex

lib/pleroma/web/mastodon_api/mastodon_api_controller.ex

lib/pleroma/web/twitter_api/controllers/util_controller.ex

test/emoji_test.exs

test/formatter_test.exs

test/web/mastodon_api/mastodon_api_controller_test.exs

test/web/twitter_api/util_controller_test.exs