Create static timer instance for UAVO browser. This single timer sets the
rhythm for all highlight events. Previously each class instance had its
own timer and this led to lots of expensives and unnecessary calls to
QTime::currenttime();
Added Qt::UniqueConnection, which ensures that the slot cannot be
connected to multiple times.
Moved currentTime to UAVObjectTreeModel. This eliminates the global and
possible race condition.
Created TreeItem class method for assigning m_currentTime. This simplifies
the number of required constructors.