Event Handler

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

src/qml/Component/NeochatMaximizeComponent.qml

@@ -87,7 +87,6 @@ Components.AlbumMaximizeComponent {
             eventId: root.currentEventId,
             source: root.currentJsonSource,
             file: parent,
-            mimeType: root.currentMimeType,
             progressInfo: root.currentProgressInfo,
             plainText: root.currentPlainText
         });