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/linkpreviewer.cpp

@@ -13,7 +13,7 @@
 
 using namespace Quotient;
 
-LinkPreviewer::LinkPreviewer(QObject *parent, NeoChatRoom *room, const QUrl &url)
+LinkPreviewer::LinkPreviewer(QObject *parent, const NeoChatRoom *room, const QUrl &url)
     : QObject(parent)
     , m_currentRoom(room)
     , m_loaded(false)