Added a test for addition of a numeric UDA
Added failing tests for removal of UDAs
Allow numeric fields to accept value of None
Allow string fields to accept value of None
Do not swallow KeyError and return field-specific null values for known fields.
DirtyableDict should be a subclass of dict, not list.
Simplifications and fixes to `Task.get` and `Task.__setitem__` to reduce surprises.
Get the DirectDB method to delete values correctly.
Remove unused import.
Remove test we decided to jettison at the end of #70.
Merge branch 'uda_handling_alterations' into develop