Move to either c++ or python, away from dual/hybrid model

[fnoop]

vision_landing is currently a python wrapper/supervisor that talks to dronecode, and calls c++ code for the visual processing.
This works, but turns out to be overly complex to coordinate the two halves, and dronecode is very slow/inefficient.
As we want to get vision_landing running on much slower platforms -ie. raspberry - migrate to:

• single code, either python or (probably) c++
• away from dronecode, to either direct mavlink or mavros connector

[kripper]

C++ is faster, but having a Python wrapper for the high level mavlink communication is not a problem, as long as the IPC (currently using stdout queues) is well designed and abstracted (like a C++ module for Python).

Please note that stdout and stderr lines may arrive in wrong order.

Also see: chobitsfan/apriltag_plnd#1

[fnoop]

C++ is faster
If python is fast enough for the job, it's a much more friendly language to code a project like this in, for others who want to experiment/contribute. My personal opinion is c++ should only be used where necessary for uses outside of the main flight controller code, because the number of people who can safely write not-to-buggy-code in c++ is much lower.

[kripper]

Agree.