Add constraint to InstanceUser to prevent duplicates

Also adds a data migration to remove any duplicates that snuck in.
Users should only have one InstanceUser per Instance.
Merge pull request #1509 from maurizi/fix-duplicate-instanceusers

Add constraint to InstanceUser to prevent duplicates
Validate default values on UDF fields.

It is convenient to specify a default value for UDFs (especially
collection UDFs), but we should validate that the default is a valid value
Handle null 'readonly' fields

plot.readonly is nullable in otm1 but not otm2
Enhance and cleanup 'save_user' function

change model -> user for readability
change ambiguous try/except block to conditional block
add documentation
add sanitation logic
fix arity bug in partial application
Add migrator support for config file over args
Stop holding all fixtures in memory

There's no need to hold all fixtures in memory. Change some code around
so that they get read into memory just long enough to be used and released.
Merge pull request #1514 from maurizi/udf-default-values

Validate default values on UDF fields.
Merge pull request #1515 from steventlamb/topic/cleanup_migrator_params

Topic/cleanup migrator params
Increase maximum photo size

10mb was chosen arbitrarily, but PTM had some approaching 20mb.
Add newlines to sanitized username characters
Update migration rules to match philly data
Merge pull request #1516 from steventlamb/topic/philly_data_massage

Topic/philly data massage
Add option to not stringify JSON parameters when calling ecoservice
Merge pull request #1519 from RickMohr/dont-stringify-json-in-eco-calls

Add option to not stringify JSON parameters when calling ecoservice
Skip failing test for now
Add Species to an instance when creating the instance.

Fixes #1492
Re-enable test (fixed elsewhere)
Merge pull request #1521 from maurizi/add-species-when-making-instances

Add Species to an instance when creating the instance.
Fix lint