Make a module for admins to quickly register Junction/Delve classes
Make programs less dependent on (Student|Teacher)ClassRegModule

Adds "is not None" check in references to (Student)ClassRegModuleInfo
in modules/base.py and modules/handlers/adminvitals.py, so that programs
which don't have a (Student)ClassRegModuleInfo can still load modules
and use adminvitals.
Add Formstack client library and some models/methods to interact with Formstack forms
Add a FormstackAppSettings module_ext to store metadata and settings for a Formstack application form
Add FsStudentApp object to store data related to a student's submission
Add FormstackAppModule and /studentapp handler
Improve error handling in Formstack client library
Trivial: add a docstring and some whitespace
Cache field info in FormstackAppModule
Move get_field_info and get_student_apps from FormstackAppModule to FormstackAppSettings for easier access
Add method FsStudentApp.get_responses that returns a list of (question, response) pairs for an app
Move get_student_apps back to FormstackAppModule from FormstackAppSettings
Cache submitted data for each app to decrease API calls to Formstack
Refactor FormstackAppModule.get_student_apps

.fetch_student_apps now does most of the work, .get_student_apps calls it and caches the result.
Add /listapps and /viewapp views for listing and viewing apps respectively
Additions to FsStudentApp model and associated views

- Add admin_status and admin_comment fields to FsStudentApp
- Add new columns for those fields, plus a column for username with profile link, to /viewapp
- Modify get_student_apps logic to not clobber values for admin_status and admin_comment
Remove FormStackAppSettings.configure() and replace with .create_username_field()

The only nontrivial thing that .configure() was doing was creating a username
field anyway, so I just factored that part out and deleted the rest.
Remove Formstack migrations

Removes schema migrations from the repo, to allow for easier schema
changes during development. Migrations will be checked in when I'm
done.
Refactoring stuff into esp.application.models

Move FormstackAppSettings from module_ext to esp.application.models
(and add an import from module_ext). Move methods .get_student_apps()
and .fetch_student_apps() from FormstackAppModule to
FormstackAppSettings.

This makes it so that all Formstack application handling occurs in
esp.application, rather than in esp.program.modules. This separates
logic from presentation and makes migrations and imports more
sane. Yay modularity!
Give FsStudentApp more direct access to FormstackAppSettings

Add a foreign key to FormstackAppSettings, since that's what we want
most of the time (rather than Program). Replace the existing foreign
key to Program with a property that gets it indirectly, in case we do
need it.