Make waveform and spectrum visualizations optional and stop installing unwanted stuff

Having those built and installed unconditionally breaks linux packaging for binary addons, because files belonging to the xbmc package would be overwritten by the addon package.
We also don't want to install addon data fluff of disabled or not even supported addons on different platforms.

Not sure what to do with Win32 and Xcode?
Might also need a test on bsd.