renaming and sharing with server global libs extender
- refactoring picture_picker images validation: still an ugly hack
but slitly less ugly, plus manage deletion
+ hosted image deletion image_handler
+ very basic image galery on item_show
+ entity description
- item show re-render on add:pictures
/!\ change_picture stops to listen to add:pictures
(was causing a bug as item_show rerendering had already deleted the view)