Update mods/cnc-classic/rules/structures.yaml

Turret no longer buildable by GDI, Guard Tower no longer buildable by Nod
Update mods/cnc-classic/mod.yaml

Update mod Name and Description
Update mods/cnc-classic/rules/defaults.yaml

Fix a building explosion sound
Merge pull request #32 from Generalcamo/patch-7

GDI/NOD defense structures for cnc-classic.
Clarify mod name and description.
Change a building explosion sound.