Bug 4394 REVISED Allow opaccolorstylesheet syspref to use an external URL

Bug 4394 REVISED Allow opaccolorstylesheet syspref to use an external URL

Previous code would only allow for an auxiliary stylesheet on the same server.  This checks for
http in the opaccolorstylesheet syspref.  If it's found, sets a different variable pointing to the
remote server location.  If not found, retains the previous css directory path.

Also modifies the description of opaccolorstylesheet in the installer files to reflect current
usage as an auxiliary stylesheet.

Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>