add include folder

Include folder contains the .pri files to include when a specific package is
needed by an other. It has been added to facilitate the package inclusion.

This commit also change ItemManager header by removing includes to Folder and
Movie, decoupling client package from the Item tree implementation.

Related methods has been removed from ItemManager.
change app folder organization

Add build, bin and lib folders to handle compilation generated objects.
Include directory contain all the public includes of the libraries generated.
add global Item management functions to ItemManager

create(Movie/Folder) methods
deleteItem method
basic search method on ID
add ItemVisitor abstract class

This class will be the base class of all the visitors running through
the Item tree. It is an easy way to handle new Item types by ignoring
them at the top visitor level.