Add ability to add custom music as soundtrack-mod.

[FalangerSeich]

Add ability to add custom music as soundtrack-mod.
There is \RESOURCE\Music\ folder in original GW and ET. Game plays files in situations according to their names.
Files of GW:
Alpha_Expedition.ogg
defeat.ogg
Empire_Covered.ogg
Empire_Military.ogg
Empire_Primary.ogg
Empire_Psychosphere.ogg
Exodus_Covered.ogg
Exodus_Military.ogg
Exodus_Primary.ogg
Exodus_Psychosphere.ogg
Fostral.ogg
Harkbackhood_Covered.ogg
Harkbackhood_Military.ogg
Harkbackhood_Primary.ogg
Harkbackhood_Psychosphere.ogg
Perimeter_Main.ogg
victory.ogg

Files of ET:
alpha.ogg
Alpha_Expedition.ogg
battle.ogg
bellstrike.ogg
construction.ogg
defeat.ogg
delusion.ogg
destination.ogg
dna.ogg
Empire_Covered.ogg
Empire_Military.ogg
Empire_Primary.ogg
Empire_Psychosphere.ogg
empire0.ogg
empire1.ogg
empire2.ogg
exodus.ogg
Exodus_Covered.ogg
Exodus_Military.ogg
Exodus_Primary.ogg
Exodus_Psychosphere.ogg
exodus0.ogg
exodus1.ogg
exodus2.ogg
Fostral.ogg
Harkbackhood_Covered.ogg
Harkbackhood_Military.ogg
Harkbackhood_Primary.ogg
Harkbackhood_Psychosphere.ogg
harkbackhood0.ogg
harkbackhood1.ogg
harkbackhood2.ogg
main.ogg
maintheme.ogg
MechMessiah.ogg
oderzh.ogg
Perimeter_Main.ogg
phobos.ogg
promised_land.ogg
psychosphere_e.ogg
psychosphere_h.ogg
psychosphere_x.ogg
regular.ogg
theme1.ogg
theme2.ogg
theme2_1.ogg
theme2_2.ogg
theme3.ogg
theme4.ogg
theme5.ogg
theme5_1.ogg
theme5_2.ogg
Theme6_F1.ogg
Theme6_F2.ogg
Theme6_F3.ogg
Theme6_S1.ogg
Theme6_S2.ogg
Theme6_S3.ogg
Theme6_S4.ogg
theme7.ogg
theme8_1.ogg
victory.ogg
wasteland.ogg

So, the idea is to create mod-type "music" and add some custom folder under mods, then add parser to parse files in subfolder.
Maybe, add proper naming rules, e.g. "musgw" and "muset" folders.
OR
Add config-based ZIP-parser. If someone wants to add custom soundtrack - he must name his files properly and put them into zip, then put into special folder for music. Also, config will be good too: if no config - game reads and plays files by names, if config presents - it is parsed and used. e.g.:
game: gw
alpha: myfile1.ogg
defeat: myfile2.ogg
exodus: myfile3.ogg,myfile4.ogg,myfile5.ogg
...

game: multiplayer
exodus: myfile3.ogg,myfile4.ogg,myfile5.ogg
...