Adds mimetypes repository

The Qt4 implementation of the Qt5 QMimeDatabase QMimeType classes. This was
the project that gave birth to the Qt5 QMimeDatabase & QMimeType classes.
libqtxdg will use it instead of libmagic on Qt4.

Upstream repo: https://qt.gitorious.org/qtplayground/mimetypes

Signed-off-by: Luís Pereira <luis.artur.pereira@gmail.com>