Support for a server-side list of 'supported buildpacks'

A supported buildpack has the following attributes: name, description, buildpack and support url.

Normal users using clients such as vmc will be able to read the list and provide it to the user for a better experience.
Admins will be able to maintain the list using clients such as vmc.
The list can be initialized by running the controller with the "-m' (run migrations) parameter and using a configuration file (the default being "config/supported_buildpacks.yml").