Update casebook.models

Change Transaction.quality to PositiveSmallIntegerField
Set Transaction.status to default to 'For Sale'
Add fixture.json with basic data
Update Admin display fields

Add readonly_fields to TransactionInline
Add list_display fields to MemberAdmin
Update casebooks.models.Transaction()

Correct posting_date
Add sold_date
Update casebooks.models.Casebook()

Add Casebook.get_transactions() to return transactions involving that casebook title
Update casebooks.models.Transaction()

Add Transaction.school to store school at which transaction is occuring
Overwrite Transaction.save() to add the seller's school to the transaction prior to saving
Update casebooks/casebooks_list.html

Add display logic to list each transaction for each book as indented list elements
Update casebooks.urls

Comment out urls without working views
Update /for_sale/ to use the TransactionListView
Update casebooks.views

Comment out function based views that will be replaced by class based views
Add TransactionListView() to serve a list of transactions at the user's school
Add TransactionDetailView() to serve the details of a transaction