NavigationPath: possibility to pop down to selected node, and add a "Root" node

Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>
Contextual properties:
 - Display the number of selected items when in multi-selection
 - For a single selection, show properties for collections, sets and photos.
 - Try to work on a generic pageModel infrastructure
Filtering:
 - possibility to define a regex filter
 - filter is applied on each item of the main view, hiding the delegates that don't match it
 - possiblity to apply filter on several properties at the same time (title, tags...)
Fixes/rework:
 - avoid processing onClick when a double-click occurs
 - crop right border of "images/panel.png "
 - regroup the app-wise properties in FlickrBrowserApp singleton (current selection, filter, active model in main view)


Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>