Patch: gtk folder store configurable with flags

[José Dapena Paz <jdapena igalia com>]

	Hi,

	This patch adds a new constructor for the gtk folder store, so that
developer can pass some flags specifying the way the folder store will
be filled.

	I added two flags:
	* One makes folder names in treemodel contain the full path, instead of
the name of the folder leaf.
	* The other one puts all the folders at the same tree level (put
folders in a list, instead of a tree).

	Both can be combined to show a plain representation of all the folders.

Changelog would be:
* libtinymailui-gtk/tny-gtk-folder-store-tree-model.[ch]:
	* Now developer can set flags on constructing the widget, to
	   specify how folders will be added to tree model.
	* One of the modes will make name column contain the full path
	  of a folder.
	* Another mode will store all the folders at the same level 
	  (show items as a list instead of as a tree).

-- 
José Dapena Paz <jdapena igalia com>
Igalia