Remove Regal and move SDL2 libraries
Initialization fixes

-add vr_svr_enable and vr_ovr_enable to control whether SteamVR /
OculusVR backends are enabled/disabled
-Add HMD information string as vr_hmdstring
-Add HMD info string to the bottom right of the console
-Simplify interactions with SteamVR API
-Cleanup init messages