Add Chromium without proprietary components, Firefox and easy settings for other apps

[jeda]

It could be configurable, and also make multiple Dockerfiles etc. to not keep it together when it'll be unused.

[jeda]

Since we're adding already some proprietary components (#58), it feels the new title would fit better.

[AznManDown]

We're not going to be able to add Firefox at the moment, given there is an issue with their policy engine. I'll keep it on my radar and add firefox support once they finally resolve that issue.

In the meantime, I'll go ahead and add options for other browsers.