Add `python-gflags` as a development requirement.

We need this in development to kick off an initial OAuth flow through
a browser session to add credentials to `tokens.dat`; once this gets
deployed, these credentials should be deployed with the app, so we won't
need the library.
Mark `manage.py` as executable.
Factor out the Google directory service.

I'm not entirely sure about where this should go, but having it in one
place seems like an improvement for now.
Recover from and report uniqueness errors on load.

This was code I added to debug a problem with the task failing, down to
the fact that `get_or_create` is using the tuple of name, email and
Google ID to match people, which breaks if people change their name (or,
less likely, change their email).

The bug is fixable, but this seemed like useful code in its own right.
Merge branch 'add-gflags'
Merge branch 'chmod-plus-x-boom'
Merge branch 'report-uniqueness-errors'
Merge branch 'pull-out-google-client'