Features: add an api for setting trace line color and thickness

[songxiaocheng]

There is a little problem that the alpha channel is not working. I also tried to manually call DrawDebugLine but the trace lines are always opaque. It seems like a UE issue, so I kept this argument. For now, setting RGB and thickness works well.

[madratman]

Can we maintain consistency w.r.t. simPlot APIs (those APIs ask for rgba list in python in 0-1 range) (see plot_markers.py)

the lines here might make alpha channel work
https://github.com/microsoft/AirSim/pull/2304/files#diff-405ee0a8e5b40c6316073f72165e0228R177
https://github.com/microsoft/AirSim/pull/2304/files#diff-405ee0a8e5b40c6316073f72165e0228R180

[songxiaocheng]

Hi @madratman, I've updated as you suggested.
As for the alpha channel problem, the two lines code you mentioned is not working either.
Actually, in my test, the alpha channel is also failed to work for the simPlot* APIs. Do you have the same problem?

[madratman]

Unable to resolved the transparency, but apart from that, it works fine.
Thanks for the contribution!

[rajat2004]

What is the range of thickness here? 0-100? and is it in pixels
Working on adding docstrings for all the APIs, so need to add this info