separate content install from loadscreen
# This is a combination of 2 commits.

# The first commit's message is:

separate content install from loadscreen

# This is the 2nd commit message:

#merge with first commit
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