Bluetooth: Audio: Media control client

This commit adds the Media Control Client from the topic-le-audio
branch.  This is a part of the upmerge of the le-audio media control
files.

This client has been developed and maintained over a couple of years
now, and is mature.  During the development it has passed both
IOP-testing and PTS qualification testing.

The commit is a pure copy of the files and content in the
topic-le-audio branch, with the following exceptions:

- files are in bluetooth/audio instead of bluetooth/host/audio, with
  some include paths updated as a consequence
- as a consequence, CMake files and Kconfig files updates are done in
  other locations
- a macro for debug output of Object ID values has been (temporarily)
  added to mcc.h, to avoid a dependency
- a blank line added after a declaration and an overlong line split,
  to pass check_compliance
- copyrights have been updated

Signed-off-by: Asbjørn Sæbø <asbjorn.sabo@nordicsemi.no>