vo_opengl: make use of newer OpenGL logging API

GL_ARB_debug_output provides a logging callback, which can be used to
diagnose problems etc. in case the driver supports it. It's enabled only
if the vo_opengl "debug" suboption is set.
vo_opengl: don't allow setting 3D LUT if unsupported

The code was always uploading the 3D LUT (even of unused), as long as
vo_opengl was setting a icc-profile. This could crash with GLES 2.
demux_mkv: use attachment filename as coverart title