Separate site information and site description #2672

Site "information" currently consists of system details computed by CMake/CTest plus a description field which is intended to be used for manual updates. There is little reason for these two things to be connected. Instead, it would be better to use the siteinformation table for auto-generated information, in addition to a separate table to store site description updates. In addition to the text of the description itself, it would be convenient to store the user who updated the description.