gstinfo: Add new maximum level debugging
gstinfo: Add new maximum level debugging

API: GST_LEVEL_MAX

By compiling gstreamer (or plugins) with GST_LEVEL_MAX defined, only
the debugging statements at or below that level will be compiled in.

This allows compiling in some debugging (like errors and warnings) which
helps in debugging, but without the full cpu/memory overhead of all debugging
enabled.

shelsonjava/gstreamer,jpxiong/gstreamer,mparis/gstreamer,centricular/gstreamer,mparis/gstreamer,centricular/gstreamer,krichter722/gstreamer,jpxiong/gstreamer,StreamUtils/gstreamer,mparis/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,shelsonjava/gstreamer,mparis/gstreamer,shelsonjava/gstreamer,centricular/gstreamer,StreamUtils/gstreamer,krichter722/gstreamer,krichter722/gstreamer,centricular/gstreamer,shelsonjava/gstreamer,mparis/gstreamer,krichter722/gstreamer,krichter722/gstreamer,shelsonjava/gstreamer,jpxiong/gstreamer,StreamUtils/gstreamer,jpxiong/gstreamer,jpxiong/gstreamer,centricular/gstreamer