Add a Grey/Orange version of the logo

[irsital]

Because we now have a proper @codestar.nl email adreses I wanted to add a small Codestar logo to my e-mail signature.

A height of 32 seems to work the best.
python3 logo.py -c all -H 32 -f png

But because of the transparency the current logo's don't look right in emails. Also I personally dislike the monochrome and light options generated.
Light:

Standard:

Dark:

Monochrome:

Looking at the email signatures of MartinW and Koen, they are using the Orange/Grey logo, which we also used on other codestar merch (T-Shirt, Mugs, Stickers).

PR #3 adds an option to generate the grey logo. I've used a color picker to find the grey value to be #9b9b9b / RGB(155,155,155), which seems to work, but we can tweak it off course.

Result in grey: