deb: package UI + pixelated

we need to produce packages for bitmask_js and our pixelated fork.

• pixelated: I think we should create a native debian package and hook the autobuild on the ci too, both for the python packages and the assets.
• bitmask_js: ideally, we could include a node compilation step in the bitmask-dev package.

However, I've been having some problems trying to add a node compilation step to debian/rules for bitmask-dev/ui. I think the fakeroot might be interfering with node paths or something, because I get errors that I don't get when I run make python-package from my working (stretch) environment.