Improved the naming of error values in the case where they're java enums, since those already have meaningful names we can use.
Updated enum error message improvement to apply to all objects, and to also show variable names for these errors.
Add test and check for null, to stop null datapoints failing in message creation
Fixed two missed unit tests that were explicitly checking the previous error messages
Simplification of theory parameter names, since format automatically deals with toString() and nulls.
Improved PotentialAssignment description with better formatting, and handling for failed toString() calls. Refactored tests into proper unit tests closer wrapping the relevant bit of this code too.
Formatting
Merge pull request #607 from pimterry/theory-enum-failure-messages

Theories failure messages describe enum arguments unhelpfully