ensime recipe and remove self-packaged files

we've completely redesigned how we distribute the codebase (which includes a large server component written in Scala).

Sources are in a new github repository and binary builds are now hosted on `bintray.com` and handled entirely in our codebase... nothing to do with MELPA anymore. This closes #1792.

Also removed dependency on `popup.el` that you were keen for us to remove.