Add AssignmentStore module.

Resolves #317, Closes #324.
Add payments app with LineItem model.

Resolves #334.
Remove unused shortcuts.
Email external officer when school registers with comments.

Resolves #325, Closes #342.
Enforce uniqueness of country and school in CountryPreference model.

Resolves #329, Closes #343.
#329 forgotten migration.
Send confirmation email to school's primary contact on registration.

Resolves #319, Closes #345.
Encode fields in UTF8 when dumping school data.
Export School ID from admin panel.
Uses unicode in assignment downloading