RTSP rewind and fastforward support (Scale option). Almost entirely rewritten a patch from K. Staring <Qdk _at_ quickdekay dot net>.

* This is untested, but shouldn't have any adverse effect at least
* Any feedback much welcomed

* updated the po-files, started some work on the German translation, a minor string fix and removal of an untranslatable string

* when possible use the PTS for GET_TIME and GET_LENGTH. Note that this isn't always reliable. If you want you can disable it.

* use intf_IntfProgress instead of intf_UserProgress to test the interaction-implementations. Additionally, it's nicer here IMO, so we might keep it this way.

Skeleton for interaction
Fix window settings save

Some files missing.

Break binary compatibility

- toggle fullscreen mode when double clicking on video.
- allow menu autoshow/autohide when moving cursor in or out the menu area while in fullscreen mode

Courtesy from Zayed Al-Saidi <zayed ÷ alsaidi × gmail ÷ com>.