Improve CI to use conda-packages and python 3.6

Our CI infrastructure for this package still uses Python 2.7!

A list of points we should consider when upgrading this:

• Python 3.6
• Use the latest beat-devel to install things like sphinx, nose, coverage and other required base infrastructure
• Install beat.cmdline, core and backend.python from our conda channel (beta) - if that is not possible, ensure this package only tests against the "master" branches of each of those
• Reduce specific package pinning to the minimal required
• buildout phase should not install anything - the file dev.yml should contain all dependencies - except, perhaps, the javascript stuff
• the scripts to build .so files on beat.core is being called from this package - maybe we should consider to distribute pre-built binaries with beat.core for such a purpose? In particular, inside buildout.cfg we call these - need to figure out a solution...