PLT-1378 Initial version of emoji reactions (#4520)

* Refactored emoji.json to support multiple aliases and emoji categories

* Added custom category to emoji.jsx and stabilized all fields

* Removed conflicting aliases for :mattermost: and :ca:

* fixup after store changes

* Added emoji reactions

* Removed reactions for an emoji when that emoji is deleted

* Fixed incorrect test case

* Renamed ReactionList to ReactionListView

* Fixed 👍 and 👎 not showing up as possible reactions

* Removed text emoticons from emoji reaction autocomplete

* Changed emoji reactions to be sorted by the order that they were first created

* Set a maximum number of listeners for the ReactionStore

* Removed unused code from Textbox component

* Fixed reaction permissions

* Changed error code when trying to modify reactions for another user

* Fixed merge conflicts

* Properly applied theme colours to reactions

* Fixed ESLint and gofmt errors

* Fixed ReactionListContainer to properly update when its post prop changes

* Removed unnecessary escape characters from reaction regexes

* Shared reaction message pattern between CreatePost and CreateComment

* Removed an unnecessary select query when saving a reaction

* Changed reactions route to be under /reactions

* Fixed copyright dates on newly added files

* Removed debug code that prevented all unit tests from being ran

* Cleaned up unnecessary code for reactions

* Renamed ReactionStore.List to ReactionStore.GetForPost

api/api.go

@@ -103,6 +103,7 @@ func InitApi() {
 	InitEmoji()
 	InitStatus()
 	InitWebrtc()
+	InitReaction()
 	InitDeprecated()
 
 	// 404 on any api route before web.go has a chance to serve it