Revert "Change to system wide rvm installation (closes GH-24)"

This reverts commit b3799d57161f8fbd4f0a5615dea4bce0f0d8bee8.
Revert "Fix ruby installation with RVM"

This reverts commit 37eab68f0e31a6f4d5e1191920cebe43f3f79ecc.
Manually manage rvm's dotfiles [GH-2]