Rename clobber to mask
Move global constants before class definition
Add more information to instance info endpoint

Most of what we want is similar to the "form_extras" tags that we use in
our templates so part of this commit refactors for edits to share code
directly with the API.

This also fixes an bug where a model without an instance but with unit
data would crash the template tags.
Merge pull request #999 from ahinz/topic/add-more-info-to-api

Add more information to instance info endpoint
Mask unauthorized fields in api including UDFs

fixes #987 on github
Merge pull request #1000 from steventlamb/topic/mask_unauth_udfs

Topic/mask unauth udfs
Serialize values for DateFields differently than for DateTimeFields
Change date styling so that a full mm/dd/yyyy can be seen.  Fixes #895
Show Date Planted and Date Removed fields on tree detail, fixes #961
Merge pull request #983 from maurizi/topic/datePlanted

Show date planted and date removed fields
Properly return dictionary
Fix in 'request.user.is_authenticated'

This is a weird bug, but not all requests have a user object attached to them. I was getting crashes when running the otm1 migrator.
Make get_last_visited_instance safe
Fix inconsistency in User save validation

Certain validation checks were only being executed when user.save() was called, leaving save_with_user() unvalidated. Pushing these validation checks into save_with_user()
Fix outdated code in migrate_otm1

Some things in the app have changed since the last time this was executed.
Make less common fields optional

Move defaults into code, out of declarative portion
Merge pull request #1009 from steventlamb/topic/misc_fixups

Topic/misc fixups
Make exception block smaller

This exception block was catching all exceptions, including ones that occured on the second line, which are not adequately explained by the message provided in the except block.
Clean up get_instance_user

Make get_instance_user more readable

By using a get() query, this will run a maximum of one query, whereas previously, for the common case where a single InstanceUser exists, two queries will run.
Add a save() convenience method to InstanceUser

For the same reasons that it exists on User