Changes

personalization: indicate default ParamSource per ConfigurableParameter

Add default_source class members pointing to ParamSource classes to all
ConfigurableParameter subclasses.

This is useful to automatically set up a default ParamSource for a given
ConfigurableParameter subclass, during user interaction to produce a
batch personalization.

For example, if the user selects a Pin1 parameter, a calling program can
implicitly set this to a RandomDigitSource, which will magically make it
work the way that most users need.

BTW, default_source and default_value can be combined to configure a
matching ParamSource instance:

  my_source = MyParam.default_source.from_str( MyParam.default_value )

Change-Id: Ie58d13bce3fa1aa2547cf3cee918c2f5b30a8b32