RESTful API for POSTing JSON Plan

[bbangert]

The Plan posted should be of the same format as in #71.

The API should require a Project name. The Plan and posted JSON should support interpolation like in #71. It'd be useful to have a few valid interpolation globals like 'UUID' so that the POST can be run multiple times to create new Plan's.

The Plan should be verified and error on adding it if the containers can't be located.