Multiple fixed events (per event type) should be supported

Limited to a single event command-line per event type (configured in SCFG->External Programs->Fixed Events) is silly: these should be lists of event command-lines (and maybe options, e.g. DOS vs. native EXE).

In main.ini, convert [*_event] sections to [*_event:index], e.g. [logon_event:0]