prefix oauth_callback path with site name

...so i can reuse my one instagram app that has a localhost oauth redirect URL. instagram only lets you set one redirect URL per app, and you only get 5 apps total, so i have to share one app for localhost testing across all of my apps, so they all need the same redirect URL. :/
drop instagram client id/secret usage since we get the access token from oauth-dropins

removes app engine dependency entirely when used as a library
readme: clarify that just the tests require app engine

also drop an unnecessary import in source_test
updated Twitter with timezones
Merge pull request #9 from kartikprabhu/twitter-tz

updated Twitter with timezones
readme: no more hard-coded app engine sdk path!
use UTC for test data timestamps to avoid dependence on local time zone

fixes #11
update webutil, mf2py
update oauth_dropins
update webutil
update oauth-dropins
update webutil
update oauth-dropins
update oauth-dropins
update oauth_dropins
update oauth_dropins
update webutil
standardize Source.user_url() method for all source classes

also use https for facebook, twitter, and G+ URLs
microformats2.json_to_html(): support multiple urls

fixes #133. cc @gRegorLove
update oauth_dropins