moving param binding helper implementations into header

[laroque]

Moving the two helper function implementations back into the headers.

This is because as source, they are used to build libraries of type MODULE_LIBRARY (which are not able to be linked). That isn't a problem for scarab itself, but means that packages which include scarab cannot link those implementations for other libs.

There is some discussion elsewhere (pybind/cmake_example#11 (comment)) about how to achieve a more desirable pattern (with headers defining the bindings themselves, but required non-trivial implementations in source files and building a supporting library that can be linked elsewhere). We don't currently have bandwidth to continue exploring those patterns.

[laroque]

As an extra note: The motivation for this change was so that dripline-python could convert back and forth between param_node and python dictionary types and thus be able to pass content into the param_node& a_config argument to many dripline-cpp classes. I tested this by assigning the alerts-exchange in a Service config in the YAML and it worked as expected.

[nsoblath]

Looks good to me