Teacher app management page improvements

[aoby]

1. Add program_registration_id column to Pd::TeacherApplications, and updated PdProgramRegistration for to supply it, so we don't have to query pegasus to know if an associated registration exists. We still query to retrieve the up-to-date form including any edits from the UI.

2. Include associated tables in the manage query, to prefetch and speed up the query (13 fold on my testing in the Rails console in production-console).

3. Add some basic paging to the manage view, because a list of 3000 applications in one page is just unwieldy even with the perf improvements.

Now the header looks something like this (with ~1k dummy applications on localhost):

Available page sizes:

Filtered:

4. Add requested ability to edit selected course for teacher applications.