Change fields that hold student course credit to three decimal places to accommodate fractional credits.

The issue came from the DE DOE, who need to represent cases where a student receives 1/8 course credit. That value is not possible to represent accurately in the 2.0 Ed-Fi standard where course credit can only hold 2 decimal places, and so can't hold the necessary value of 'n.125'

The underlying simple type that would need to change is CreditsValue, increasing decimal places to 3.

Original report was via GitHub here: https://github.com/Ed-Fi-Alliance/Ed-Fi-Release/issues/672