[nim, brain] #19 Adds enpoint for adding distribution plan without line items
[nim, brain] #19 using 'line_items' instead of 'items' in distribution plan to avoid confusion
[nim, brain] #X Makes all models we have so far editable with the admin site
[nim, brain] #19 Can add dist plan line items to plan through API.
[nim, brain] #19 Renames 'distribution plan item' to 'distribution plan line item' for clarity. MIGRATIONS LEAVE THE OLD TABLE BEHIND. Bug in django migrations