Reorganizes common OAuth2 things into importer/oa2_importers.go
Rewrites CallbackURLParameters to return url.Values.
A controversial workaround for nil context has been left out,
and this may cause panic and will need a proper fix.
Change-Id: I0789f4732412aa559078ec2c6b6797925ab8cd05
Imports all images from all albums, and puts each image in its album.
Each album is linked under "Picasa (<username>)".
Tries to skip already imported files (check based on album/filename).
See Issue #391.
Change-Id: If00751671a429891c05bbe41f59c1421b2ff2de8
Brad Fitzpatrick