Add icecat

[SolidHal]

I've put some work into getting icecat to build on armhf, which can be found here https://github.com/SolidHal/icecat-arm

Now need to figure out how to install and/or package as a debian package and install.

This is necessary as firefox doesn't have fsf approval.

[albsod]

Cool! Did you know that Icecat is already available for armhf-linux in the GNU Guix project and that they regularily apply security patches from upstream.

[albsod]

Oh, I see that Guix's armhf build is failing currently.