CDA backend has been ripped off!

CD-Audio support has been removed in favor of OGG music. This
required several changes on code:

* OGG music is enabled by default (if HT_WITH_OGG is defined)
* Related source files and references have been removed
* There's no more 'cd_shuffle' cvar
* Persistent 'shuffle' setting on menu
* Fixed bug that caused crash when toggling shuffle on menu
* Some cleanup of the OGG backend