[bug 965794] Add Product table

* add product table model
* add schema migration
* add data migration adding initial products
* add product admin (we'll use this for now)

This is for this bug: https://bugzilla.mozilla.org/show_bug.cgi?id=965794

Pretty sure it covers all the things I need to use the Product table for. Amongst other things, this should let me remove a bunch of hard-coded stuff.

Quick r?