Add next course to countdown; code cleanup

Added the next course to be run to the "next race" countdown at the end of a race. Notably, this required the merging of cRaceManagerMode and cModuleMode.

Also improved the messages shown during database migration in order to better inform the user about the current progress of the migration.

Did some tangential clean-up of shared/_init.lua to more accurately reflect the current JC2-MP API. table.find was removed as JC2-MP has had this function for over a year.