adding new "describe_api" and "describe_admin" command

describe_api assumes the user uses the Tastypie framework

describe_api's features: 
- creates relations to the other resources based on the foreign keys in the models
- allows full filtering on all fields by default

describe_admin features:
- search fields, list_filter, list_display have good new defaults
- raw_id_fields is used for all relational fields to improve performance when using big tables