Upgrade Python modules

* App Engine SDK 1.8.4 -> 1.9.3
* `SQLAlchemy` 0.8.4 -> 0.9.3
  - required removing use of deprecated `AbstractType` base class
* `Flask` 0.9 -> 0.10.1
  - required adding `itsdangerous` dependency
  - Flask 0.10 no longer allows overriding identical URL paths via
    `app.route`, so moved `ggrc_gdrive_integration.views` view
    registrations into `init_extra_views` method.  (This should be done
    in general to avoid import side-effects).
* `Werkzeug` 0.8.3 -> 0.9.3
* `itsdangerous` none -> 0.24
  - required by Flask 0.10 for JSON
* `Flask-SQLAlchemy` 0.16 -> 1.0
* `Alembic` 0.5.0 -> 0.6.4
  - now with index and constraint inspection!
Merge pull request #1279 from reciprocity/feature/upgrade-python-modules

Upgrade Python modules