feat (mongoose): use mongoose-bird to promisify the mongoose API

This is a rebase of @pentateu's mongoose-bird PR, rebased onto `canary`.

Main purpose is to demonstrate the rebase changes. Can be closed in favor of #503.
@kingcody  I noticed that you have removed the <% if (filters.mongoose) { %> from around the var Thing = require('./thing.model'); ... and in some other places also.

This is required so when the mongoose option is turned off in the generator this line is not generated in the final output.