Add API for updating models
Fix bug where new objects weren't being created

Previously if a user with enough permission to create an object (all
required fields) but lacked wire directly on all fields (such a 'plot
length') the object would be marked as pending and not created.
Support using full_clean[_with_user] for validation
Update UDF support to validate only on save

Also include UDF support in plot/tree editing
Support adding trees and plots
Merge pull request #227 from ahinz/topic/add-edit-plots-api

API to add plots and trees