enable VNC on selenium grid via config

[tobysoby]

Hey, thanks for this great product!

We currently use galen for extensive tests on a selenoid powered selenium grid. Selenoid offers the possibility of VNC, which we use in the early stages of spec development for debugging etc. This is enabled via the capability "enableVNC". I know that I can use a custom capability when I instantiate galen from js tests, however we use the "regular" setup with a galen.config. I haven't found a way to tell galen via the galen.config to launch a browser on grid with the capability "enableVNC".

Right now we use a patched version of galen enabling that feature, something we would love to see in the mainline. I created a small PR for that (#620). Would you consider having that feature in the mainline? If there is anything missing from your point of view please don't hesitate to say so!

Thanks again!