Added option to define step values for grid labeling

[djhoward12]

Added option to define step values for use in the labeling of FloorPlan Grids. Updated documentation and tests.

[smk4664]

Please see comments on implementing Custom Validator instead of having it in the save method.

[joewesch]

@smk4664 are we good to merge this one yet?

[smk4664]

Thanks for the changes! I offered a suggestion on how to implement the validator as a class, but this is optional.

[smk4664]

Not blocking, but to get around the validate_not_zero.message and follow established Django Pattern, you can change this to a class. In case you need this in the future.

Suggested change

	def validate_not_zero(value):
	from django.core.validators import BaseValidator
	class NonZeroValidator(BaseValidator):
	"""
	Ensure that the field's value is not zero.
	"""
	message = "Must be a positive or negative Integer not equal to zero."
	code = "zero_not_allowed"
	def __call__(self, value):
	if value == 0:
	raise ValidationError(
	self.message,
	code=self.code,
	)