Feature Addition: Group Syncing

[sillywilly42]

Based on implementation suggestion by Justin McWilliams: https://groups.google.com/d/msg/simian-discuss/2CNN5EvaRWs/MpeetxHkDUEJ

If this pull request gets merged I'll take a stab at updating the API documentation to include an example client script.

This change creates a new Manifest Modification type: group. There's a group model which is just a list of owners (strings). I created a new API for creating, updating, viewing, and deleting groups. And the web interface has been updated to include groups. A lot of the code is just duplication of the Tag code since Tags are to uuids what Groups are to owners.

Most changes support this new feature, however the following additional changes were also made:

• src/simian/mac/common/auth.py - added scope string. I could not make oauth with a service account work without this. I think something has maybe changed on the appengine backend?
• src/simian/mac/client/flight_common.py - the client parses the output of last to work out the most frequent user, on new machines that could be ‘reboot’ under certain conditions.

[maximermilov]

Thank you. merged with minor fixes. ( https://github.com/google/simian/commit/7a67c521280ef81ee0fcf689b7566df02639b4fb )