digikam: improvements

 -  Now usable in non kde desktop environments.

    Build a immutable sycoca database and use
    wrappers to tie programs to this
    database and avoid interference from the
    outside by specifying a fixed `KDELIBS`
    and fixed/empty `XDG_DATA_DIRS`.

    Added missing dependencies to syscoca
    database so that the program is complete.

    Added all build time optional packages.

    Kipi-plugins now properly detected. Added
    almost all optional dependencies so that
    almost all plugins are usable.

    Now with vlc phonon backend for video playback.

    Now with ffmpeg thumbnailer for video items
    thumbnail creation.

    Now run without any error log.

Tests:

 -  Ran most features of the standard program. Everything
    work perfectly without error logs.
 -  Ran some of the kipi plugins. Work fine there too.
 -  Ran face detection and fingerprint generation
    successfully.
 -  Oxygen icons are now displayed properly.
 -  Ran other wrapped executable successfully.