Add mapper

Ger rid of static ids for interfaces and replace with something we can
register dynamically
Implement logger.

spa/lib/meson.build

@@ -3,6 +3,7 @@ spalib_sources = ['audio-raw.c',
                   'control.c',
                   'debug.c',
                   'format.c',
+                  'mapper.c',
                   'port.c',
                   'props.c',
                   'ringbuffer.c',