Building Linux Bundles

There are too many Linux variants for ChimeraX to have a separate binary distribution for each variant. So we have settled on a common build environment for bundles. For the distributions we do, the prerequisites are compiled per-platform, and the ChimeraX code is all compiled with the common build environment.

TODO: place corresponding singularity image on singularityhub

ChimeraX Release	Build Environment
Chimera 0.9*	CentOS 7 with devtoolset-3
Chimera 1.0	CentOS 7 with devtoolset-3