Add G-Force to API and Chart

What is it?
========

This PR simply adds `v.geeForce` to the API, to allow monitoring the acceleration of your vessel. It is also displayable in the charts of the console-window.

Changes
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* add `v.geeForce` to API
* rename chart-element **G-Force** to **Sensor G-Force**
* add chart-element **Vessel G-Force** (based on `v.geeForce`)