Store a relative url to the image in the database, instead of the absolute url

This should fix display of images on remote storage groups but not yet
generation of thumbnails from remote storage. That will be addressed
by further commits.
Fix an apparent copy&paste error.  Refs #11885
Add the OpenGL2 painter to the options in the Appearance settings, make it easier for people to try it out with the aim of making it the default in future.
Reflect the use of the different painters in the log
Rename constant for consistency-sake
Make mac use new OpenGL v2 painter
Move the Gallery thumb generator thread class to libmythmetadata so it can be used by mythbackend and mythmediaserver
Remove unnecessary command option, all we are doing is adding —nologserver twice
Revert "Properly propagate quiet log option"

This reverts commit a74baed2bbf3a72f2af58fe684398d3fdd01f256.
Update SCHEMA_VERSION in perl/python bindings after e22dcf1.