don't add models to AnP model groups
don't show model group in view command
Remove ModelGroups from AnPs

CHANGELOG: As of this commit, Analysis Projects no longer have
an associated Model Group. The canonical source of Analysis Project
membership for Models is a bridge table in the database. To filter
Models based on Analysis Project you can use the analysis_projects
accessor in your commands. Ex: genome model list
analysis_projects.name='My Project'
Merge pull request #265 from acoffman/stop_creating_anp_model_groups

Stop creating AnP ModelGroups