mkvtoolnix: updated to 47.0.0

Version 47.0.0 "Black Flag"

New features and enhancements

* mkvmerge: chapters: mkvmerge can now read chapters from DVDs if the user
  specifies the path to a DVD folder structure via the `--chapters …`
  parameter. By default chapters from the first title will be imported. This
  can be changed by append `:<title number>` to the file/directory name in the
  `--chapters …` argument, e.g. `--chapters /srv/dvds/BigBuckBunny/VIDEO_TS:3`
  This feature requires mkvmerge to have been built with the `libdvdread`
  library.
* mkvmerge: added `--engage append_and_split_flac` that enables mkvmerge to
  append and split FLAC tracks, restoring pre-v45 behavior.  The resulting
  tracks will be broken: the official FLAC tools will not be able to decode
  them and seeking will not work as expected.
* MKVToolNix GUI: multiplexer: added support for mkvmerge's new support for
  reading chapters from DVDs if both have been built with the `libdvdread`
  library.
* MKVToolNix GUI: multiplexer: when deriving languages from file names the GUI
  will now look for simplified language names instead of the full ones
  (e.g. instead of looking for "Greek, Modern (1453-)" it would simply look
  for "Greek").
* MKVToolNix GUI: multiplexer: the options in the "additional command-line
  options" dialog are now sorted alphabetically. Additionally the
  `--append-mode` option has been added as one of the only missing global
  options.
* MKVToolNix GUI: chapter editor: the chapter editor can now read chapters
  from DVDs if MKVToolNix has been build with the `libdvdread` library.
* MKVToolNix GUI: header editor: added an option in the preferences for
  displaying all date & time values in UTC instead of the local time
  zone.

Bug fixes

* all: fixed a crash when using the `MTX_LOGGER=file` syntax for logging debug
  messages without specifying a file name to log to. It will now log to a file
  called `mkvtoolnix-debug.log` in the system's default temporary directory,
  as initially intended.

Build system changes

* The [`libdvdread`](https://www.videolan.org/developers/libdvdnav.html)
  library will be used if found via `pkg-config`. If it is found, support for
  reading chapters from DVDs will be enabled in `mkvmerge` and the MKVToolNix
  GUI.
* Boost's Date/Time, Lexical Cast, Range, Range Adaptors, Tri-Bool, Variant
  libraries are not used anymore.
* MKVToolNix now requires a C++ compiler & standard library that support the
  following features of the C++17 standard: "`std::variant`", "`std::gcd`".
  For the GNU Compiler Collection (gcc) this means v7 or newer; for clang it
  means v4 or newer — the same versions required by earlier MKVToolNix
  versions.
* MKVToolNix now requires version 6.1.0 of fmtlib or later for the
  `fmt::to_string` function and bugfixes to the formatting of floating point
  numbers. If a system-wide version is installed that's older, the bundled
  copy will be used.
* The bundled version of fmtlib has been updated to release 6.2.1.


(adam)