Move src to cura so we can use the same package for installed and source

Contributes to #41
Contributes to #42

cura.py

@@ -3,7 +3,7 @@
 # Copyright (c) 2015 Ultimaker B.V.
 # Cura is released under the terms of the AGPLv3 or higher.
 
-from src.CuraApplication import CuraApplication
+import cura.CuraApplication 
 
-app = CuraApplication.getInstance()
+app = cura.CuraApplication.CuraApplication.getInstance()
 app.run()