Provide hookup point to attach to external data provider for function parameters

[artemdinaburg]

Right now we rely just on Binary Ninja or IDA to provide all knowledge about a function.

We should be able to add external sources of information! Like, sometimes we have source code. Or someone can manually edit in a definition.

In more specific terms: we should add code in bnprogram.py:_get_function_parameters to consult an oracle of some kind about what functions parameters are for a specified function.