Fix backward-compatibility with vlc 2.x and solve some issues with
mouse wheel and DVD menu navigation:

-   Start using TravisCI for test builds
-   mediawidget: Override DVD keys instead of changing their settings
-   mediawidget: warn user to use keys for DVD menu
-   mediawidget: remove a now uneeded check
-   mediawidget: fix video position movement with mouse wheel
-   mediawidget: fix the mouse wheel behavior at the streaming window
-   vlc: with vlc 2.x, use vlcMedia for libvlc_MediaMetaChanged event
-   vlc: fix support for vlc 2.x

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>