Picasa: add importer.

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
Merge "Picasa: add importer."
website: add Picasaweb to 0.8 notes

Change-Id: I0de6dbfa506a9153a73c61e638ce4ddbfbfde702
more TODO

Change-Id: Ibb03612c1a06287bf781b96f478d4d627b159c84
genconfig: picasaa importer doesn't have a path

Was removed during codereview, but not removed from here.

Change-Id: I51309f46fe9747bcc0b2476813acac9120c32b28
TODO: ditch the importer.Interrupt type

Change-Id: I3a7eac29713a5079220b2e56508bd8ca105b14cf
HACKING: update github part

Change-Id: I1e8bc0381a084357dd0a008a1a1e2563f85a9ea6
storagetest: add a test of EnumerateBlobs w/ prefix of a blobref

Change-Id: Id865da5ba6c65e0110b0eb6c6d0bd45980d33105
Merge branch 'master' of https://camlistore.googlesource.com/camlistore