unify install from CD logic
unify music install and add a download option

closes #4759
fix Tiberian Dawn CD rip logic

closes #4424
add TrimOrDefault to avoid NREs
unmount all to avoid write permission problems

fight the new caching mechanism and M$ WindowsTM file systems
don't check for general.mix as it stays unmounted

however still extract it
don't test for scores.mix as it is optional
Intro/Map music is also split across several files here
restart the game instead of unmounting on the fly

avoid more redundancy between the load screens
save a redirect