Transition: Properly emit sourceStateChanged

Change-Id: I98ecbd6d18419a9d53b2e2fef474ae0a6380edaa
Improve tracking of edges on movement

Change-Id: I8314498d396c341a66d5848adb26bf69f3a19e52
Improve method of semantic zoom

No longer scale the whole scene, instead linearly transform the elements
of the scene.

=> Borders of non-transition-based items are no longer
enlarged/shrinked
=> Text no longer enlarged/shrinked
=> Hide contents of elements in case they get too small

Change-Id: I138af6f13279f5adfe2913838b320b24175c7372