Update spack-manager directory structure

[psakievich]

We really need to clean up spack-manager's directory structure. One option would be the FHS like spack: https://en.wikipedia.org/wiki/Filesystem_Hierarchy_Standard

I'm a little torn because it would be good to move to a standard but I also think it makes things a little less obvious.
At the very least we need to clean out a lot of the unused directories from the gitrepo and organize things so that exawind specific code is grouped together.

[tasmith4]

I would vote against the FHS. I have struggled a lot with both spack and exawind-builder precisely because they use this layout, and it requires some mental mapping to know where everything is.

I think we can do much better by having names that are unique to this repo and clearly communicate.