separate content install from loadscreen
unify install from CD logic
unify music install and add a download option

closes #4759
rebase bit rot crap
fix Tiberian Dawn CD rip logic

closes #4424
add TrimOrEmpty 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
fix the music list not being populated after CD asset install
remove non-existing "INIT_SETUP" chrome widget reference
rename gameinit to install for consistency
prevent flickering
consistent size for all install panels
Let FieldLoader do the hard work of loading fields.
fix Tiberian Sun installation from CD
@pchote breaks all the things