Update build framework to latest conda-forge linux-anvil and conda 4.4+

[jchodera]

At this point, we should start to drop Python 3.5 and migrate to a more modern build image based on conda 4.4+ and the latest conda-forge build images.

[Lnaden]

This is an ongoing conversion, starting in the dev builds at omnia-md/conda-dev-recipes#154. I'l be able to circle back to that this week.

[jchodera]

That would be awesome! I'm happy to help finish this up, but since you already have a great start, it would be ideal if you could push things a bit farther and leave me a list of things that need to be cleaned up.

[Lnaden]

Will do.