MAVExplorer requires dependencies that don't come with MAVProxy

Installing MAVProxy with pip will install several dependencies, but it doesn't install either `wxPython` or `matplotlib` both of which are required to allow MAVExplorer to work. Given that MAVProxy is frequently used on headless machines a better solution might be to distribute MAVExplorer as it's own package (unless there are other things I'm missing that would also improve this).

It mostly just leaves the user in a guessing game of which python package provides the missing import (which is more annoying for wx then matplotlib)

No file or test is named. Start by inspecting MAVProxy's Python dependency metadata and the MAVExplorer entry point, then reproduce a pip installation on a headless machine; done means MAVExplorer's required packages are installed or its separate packaging is clearly defined without burdening headless users.

Written by the indexing model from the issue text.