Build graph: rebuild when YML and Python sources are edited

[sgherbst]

I noticed that some build graph outputs are not rebuilt when the corresponding YML configs or Python sources are edited. For now, my workaround is to clean the build folder and rebuild everything, but it would be nice if the tool could automatically rebuild as necessary. Examples:

• Build everything, then edit a parameter in an FPGA model *.yml config -- model does not get rebuilt
• Build everything, then edit the Python code of an FPGA model -- model does not get rebuilt (similar comment for adapt_fir; in that case dependent products like the channel model would have to be rebuilt as well)

[sgherbst]

Looks like this is partially fixed -- editing *.yml files in config folder does cause code to be selectively rebuilt. However editing dragonphy/adapt_fir.py or dragonphy/fpga_models/*.py doesn't have a similar effect. But I wonder if we really need that level of specificity, since rebuilding is fast -- maybe it's enough to say that if any Python code is updated in the dragonphy folder, we rebuild everything.