Check for user adding attribute before callling fit() in safe models

[jim-smith]

probably need to create a list of what attributes are expected to be present then simply check keys in self.dict against that list

[jim-smith]

• I've had to add self.base_paramnames in that constructor to list the valid params
• Could change that to be a dict with keys for parameter names and vals holding types?
• Just then need to make al list of ther valid attributes (and their types?)