Use C++ bindings for comms protocols in GUI

[martukas]

With #1299, we have a sustainable way of generating, maintaining and improving on the communications protocol. There are a couple more improvements that can be done to further declutter the repository of third-party code as well as improve the robustness of application code.

Use C++ bindings for the communications protocol. The common.sh generate command now creates C++ bindings that it places in the GUI code tree. The GUI should use these bindings instead of the C-bindings found under common/generated_libs. They will have stronger typing and better static checks. It is also possible that ProtoTraits will be rendered unnecessary either because of this, or it may be doable by bringing in some protobuffer utilities via Conan. At least Nanopb appears to have a Conan recipe, though I have not found a ready-made package for linking.