Switch database to postgresql.
Add models.

Adds College, Meal, and `Menu Item'.

In `Menu Item', the price is stored as an integral number of cents /
pence.
Add `money-rails' gem for storing / converting money.
Change Models to reflect typing.

`type' is a reversed keyword, so this changes it to a more descriptive
type, like `food_type' or `meal_type'.
Add AR assocations between models.

Previously, only `belongs_to' associations were defined. This adds the
`has_many' association the other way, so we can create, say, Meals from
a College.
Change test users down from 50 to 10.