Getting rid of qal functions

From now on, there's no such thing as QAL as we used to know it.
htq2's QAL implementation are just defined symbols of equivalent
OpenAL functions, so that means htq2 uses OpenAL directly and NOT
through function pointers. This implementation has been based on
ioquake3's QAL in which is optional.
Introducing 'al_strings'

New command 'al_strings' is the equivalent of 'gl_strings' for OpenAL
backend
Doing several OGG fixes

Proper inclusion of OGG/Vorbis support
Default values instead of forced ones for Windows and OSX

CMake switches defaults remain as options rather than forcing them to
TRUE in every configuration
Merge branch 'qal'