Added pdbfixer recipe

I've added a recipe to build the [pdbfixer](https://github.com/simtk/pdbfixer) package from the current github master.

Once pdbfixer is stable, we can change this to build from a stable release.

This PR also eliminates the ugly `ambertools` build and source tarball, since we now have the elegant and compact `ambermini` package.

More generally, we need to figure out how to manage and build both (1) stable releases, and (2) current github masters.  It would be great if we could rig `travis-ci` for each project to also trigger a conda build + binstar upload the current github master for that project as a `master` or `development` version so that we can test against these continually, while we could build stable releases more or less manually.