Please test experimental AppImage in preparation for 5.3.3 release (esp. Python & PHP)

[Friedrich W. H. Kossebau]

Hi,

played around last night with our custom KDevelop AppImage creation, and 
managed to do one with some updated dependencies \o/

Please help by testing it a bit to see if this works good enough. Especially 
WRT Python & PHP, where I have no usage experience myself.

Get it from
	 https://files.kde.org/kdevelop/
(possibly will see a few versions, just look at the date and file name, right 
now there is only KDevelop-5.3.3pre-x86_64.AppImage)

When it comes to Python, the deps built into the AppImage possibly could get 
bumped to some newer version as well, but that needs input from someone who 
is into Python. "3.6.7" is what is used in the appimage build (not sure 
exactly if something ends up in the final appimage itself and if important or 
not).

See the related merge request where updated guide how to appimage kdevelop 
and the newer dep versions are set:
https://invent.kde.org/kde/kdevelop/merge_requests/35

Cheers
Friedrich