Currently we effectively create the reactions list in EventHandler then pass that data into a model. This reworks the model so that we just pass in a room and an event and it grabs it's own data. This means that:
- the functions in event handler are no longer required
- the model can update itself to add/remove reactions so no need to handle that in MessageEventModel
- MessageEventModel only needs to create new ReactionModels or remove old ones when no reactions exist anymore
A basic test suite has also been created for the ReactionModel
This MR deals with only sending threaded messages. Showing threads will turn up in a follow up. This allows you to start a new thread by clicking reply in thread to a normal message.
You can also do a threaded reply to a threaded message in the main timeline at the moment because those messages aren't shown in a separate thread timeline yet but will be in future.
Similar to text handler, pull out the disparate array of functions which format information from an event ready for display in the UI and put in a handler class with a test suite.
requires https://github.com/quotient-im/libQuotient/pull/686
