Include headers relative to source root directory
Move commands to cmd/ subdirectory
Move graphic item sources to item directory
Move model files to subdirectory
Move widget classes to subdirectory
Move events to subdirectory
Move item delegate classes to subdirectory
Move mime data classes to subdirectory
Move tasks to subdirectory
Clean up included headers in 'cmd'
Clean up included headers in 'data', 'delegate', 'event', 'item' and 'model'
Clean up included headers in 'task', 'test' and 'widget'