Refactor reactions

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

autotests/eventhandlertest.cpp

@@ -67,8 +67,6 @@ private Q_SLOTS:
     void nullMediaInfo();
     void linkPreviewer();
     void nullLinkPreviewer();
-    void reactions();
-    void nullReactions();
     void hasReply();
     void nullHasReply();
     void replyId();
@@ -423,23 +421,6 @@ void EventHandlerTest::nullLinkPreviewer()
     QCOMPARE(noEventHandler.getLinkPreviewer(), nullptr);
 }
 
-void EventHandlerTest::reactions()
-{
-    auto event = room->messageEvents().at(0).get();
-    eventHandler.setEvent(event);
-
-    QCOMPARE(eventHandler.getReactions()->rowCount(), 1);
-}
-
-void EventHandlerTest::nullReactions()
-{
-    QTest::ignoreMessage(QtWarningMsg, "getReactions called with m_room set to nullptr.");
-    QCOMPARE(emptyHandler.getReactions(), nullptr);
-
-    QTest::ignoreMessage(QtWarningMsg, "getReactions called with m_event set to nullptr.");
-    QCOMPARE(noEventHandler.getReactions(), nullptr);
-}
-
 void EventHandlerTest::hasReply()
 {
     auto event = room->messageEvents().at(5).get();