Capitalization, list model and room header work

- Standardized capitalization for variables and file names everywhere in
  QML and JS, get rid of mixed camelCase/snakeCase,
  use camelCase like everywhere in Qt

- ListModel items are now stored and returned as real QObjects with
  PyQt properties and signals.
  This makes dynamic property binding a lot easier and eliminates the need
  for many hacks.

- New update(), updateOrAppendWhere() methods and roles property
  for ListModel

- RoomHeader now properly updates when the room title or topic changes

- Add Backend.pdb(), to make it easier to start the debugger from QML

harmonyqml/components/pages/HomePage.qml

@@ -1,9 +0,0 @@
-import QtQuick 2.7
-import "../base" as Base
-
-Rectangle {
-    Base.HLabel {
-        anchors.centerIn: parent
-        text: "Home page"
-    }
-}