Reduce the number of possible locations used to find libraries,
to simplify troubleshooting.
Only keep '*_ROOT_DIR' and the path used by 'install_deps.sh'.
Sergey.
- rename WITH_EXTERNAL_AUDASPACE to WITH_SYSTEM_AUDASPACE.
- rename C/PYAUDASPACE to AUDASPACE_C/PY
- simplifying cmake defines and includes.
- fixing include paths and enabling WITH_SYSTEM_AUDASPACE for windows.
- fixing scons building.
- other minor build system fixes.