inventory.Organization.is_valid() function
allow overring level in Organization.analyze_store()
check update_store kwargs against STORE_FIELDS
fix type checking in inventory.add_collection()
replace inventory Organization.create with clone/init functions

Our workflow is built around clients asking Gitolite to create
repos on the server and then cloning them, rather than creating
them on the client and uploading them.
change order of inventory function args; add more docstring docs
fixed importing and var names in commands.sync_group
remove the "here (...)" from local repository label
moved inventory objects to DDR.models; updated inventory functions

Moved the inventory Repository, Organization, and Store object
code to DDR.models, to better separate it from inventory functions.
Updated the functions to actually do what we want to do. :)
walkthroughs for common inventory actions

- Set up a new Organization
- Set up Store on existing drive
- Set up new Store
- Sync new Store with existing one
Walkthroughs were tested and they actually seem to work!