Add new tables to track applicability data for a repo and a profile.
Merge branch 'applicability-performance' into rbarlow-applicability_db_models
Modify the RepoProfileApplicabilityManager to have filter() and get() support.

Also, adds full test coverage to the manager and the model.
Remove the id attribute from the RepoProfileApplicability class in the constructor.
Merge pull request #532 from pulp/skarmark-applicability-performance

platform changes for new calculate_applicable_units api, get_repo_units conduit method and unit tests