Docs: EFX relative mode
Fixtures: Fixed Venue fixture caps

Docs: Reduced size of EFX doc images
Plugins: build OLA only if present in the system
EFX relative mode doc (Thanks to George Qualley)
Fxtures: fixed Stairville HL-x9 Quad Color Flood name
Engine: increased audio buffer size

This fixes audio playback on Windows
Improved sndfile PCM format usage