Fix project implementation and project bar.

 * Change implementation of Projects adding a
	new properties name, number_of_messages,
	number_of_translated, number_of_untranslated
	and number_of_fuzzy. The path property has being
	reimplemented to include the scan of the files
	of the setted path and two new signals named
	file_added and project_changed has been added.
 * Change the implementation of FileListWidget to add
 	a row when a file is added. This should fix #10.
 * Implement project percentage bar using the new created
 	project properties.