Add a top-level Window as the root qml object

Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>
Fix bugs related to Flickr login

Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>
Collections improvements: 
 - Rework selection handling
 - Better icon quality for photosets
 - Fix bug in SingleDoubleClickMouseArea preventing the retrieval of the "mouse.modifiers" property

Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>
Collections: move delegate structure to a separate common QML file

Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>
ContextPanel: add notes about undocumented collection edtition Flickr API

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