Improve find in GenericTree to use PersistentUnit information
Set child structure update flag only for moved or stationary changes
Fix a bug in find for inexistent persistent unit guess
Add functionality to reset value and remove/detach a GenericNode
Implement core functionality of Merge / Fix flag marking of Diff

Diff:	- Modified constuctor to fix a memory related bug
	- Trees are now stored as shared_ptr
	- Improve marking of child structure update

GitRepository:
	- Adapt Diff calls
	- Improve support for Merge

Merge:
	- Implement core merge funtionality
	- Improve interface
	TODO:
		- Detect and mark conflict regions
Add CMerge command