Added access to favourite photos in viewer
Added management of favs in viewer model module
No exception on access to item non-existing in viewer model just return none
Some pep8 and cleaning in viewer model module
Added funcs for adding and removing from favs
Added func for including favs into the libary
Added handlers for adding and removing favs
Added handlers to viewer json
Activated favs in data sources widgets
refs #1091 #1092
Add photos to favourites on-line
Include all favs only on application start
refs #1091
Provided security means for photos loading
refs #1092
Favourite photos in an object oriented way
refs #1092
Favs invulnerable to the lack of records
refs #1092
More complex handling of fav photos by favs storage object
refs #1114 #1116
Added docs to favs related audio library method
refs #1115
Merge branch 'master' into favs

Conflicts:
	pisak/widgets.py