Pulp

As discussed over in https://pulp.plan.io/issues/2086#note-6, we stashed the new django code in the pulp.platform namespace. After a discussion earlier today about what to call pulp's django apps in platform and the plugins, we came up with the pretty simple scheme of <project>.app, since it's a short name and at least in the django context is a clear reference to this being a discoverable django app in django's app framework[0]. So, the pulp platform django app (currently named pulp.platform) should instead be called pulp.app, pulp_rpm's django app will be pulp_rpm.app, etc.

We'd like to do this sooner rather than later, which means we'd like to see current open pulp 3.0 PRs[1] get merged before making the switch so that the open PRs don't have to adjust to the coming change.

[0]: https://docs.djangoproject.com/en/1.8/ref/applications/
[1]: https://github.com/pulls?q=is%3Aopen+is%3Apr+user%3Apulp+label%3A3.0