Latest stable AppImage

[Jean-Baptiste Mardelle]

Hi all,

I just uploaded the latest AppImage candidate for the stable branch(18.04):
https://files.kde.org/kdenlive/unstable/kdenlive-18.04-rc.AppImage.mirrorlist

This AppImage includes all the latest fixes:
* Fix regression in 17.12.3 breaking fades and geometry keyframes on resize
* Fix startup crash in some configs
* Fix luma in wipe transition not found after saving project
* Stop warning about missing app for DVD
* Fix lowres icons on High DPI
* Fix download resources (render profiles, etc) sometimes broken
* As well as the latest MLT version fixing the alpha transparency of some 
10bit YUV formats.

Translations are missing, I hope to get them back for the final 18.04 
release.

Please test and report problems quickly so I can maybe improve the AppImage 
for the final release (19th of april).

Regards
jb