By default, numeric_base = None, to indicate that there are no explicit
limitations on the number space.
For parameters that are definitely decimal, set numeric_base = 10.
For definitely hexadecimal, set numeric_base = 16.
Do the same for ConfigurableParameter as well as ParamSource, so callers
can match them up: if a parameter is numeric_base = 10, then omit
sources that are numeric_base = 16, and vice versa.
Change-Id: Ib0977bbdd9a85167be7eb46dd331fedd529dae01
03e17a7366