Improve API when switching between buildpacks.

Also extend serialization so that it could handle null object patterns.

Refactor buildpacks into first class objects, and move logic of creating staging message to those objects.

Added API test for buildpacks.
Move rspec to test group and clean up the rake tasks that we are not using.
Removed AR connection envs
Fix typo
Added API documention for buildpacks
Added documentation of default delete behaviour to API specs
Added API documentation for posting an admin and remove key from external API
Added API documentation for posting an admin buildpack