twitter importer: meaningful names for permanodes

Make meaningful titles for created permanodes, simplified.

Change-Id: If0575b5c0ffec037feb8ce74e46f66556c582372
importer/flickr: set DateCreated attribute

Also cleaned up a few vars.
Moved some attributes to nodeattr pkg.

Change-Id: Iea496d50b12e67132fe88f371a89534c2fe32761
third_party/picago: update to 748d17b605ea675a56859678b1b0a57b38d082d0

Fixes off by one error.

For reference: picago was first vendored in at camli ref
65fa5d6d3e1e786d9960a636be6a3570105be2db

Change-Id: Id58e067a4f89199e9b20cea834bccac5decfac89
Merge "twitter importer: meaningful names for permanodes"
twitter: fix compilation error from 98a73d966d
nodeattr: fix up comment style

And use nodeattr.Title in twitter.