mobile: android splash screen (and issue 513) opacity weirdness

[Jan Mulder]

While investigating issue #513 ([Bug] Mobile: Startup splash screens 
display 2 different background color (Black then White) I found the 
commit that introduces this splash screen stuff (04e994b57558ed9). 
First, let me reset the complexity on GitHub from low to high :-) as the 
issue is related to the app bootstrap phase on device, and there is 
exactly one color defines in that whole process (which is white 
background), so where the black background phase is coming from is still 
is a mystery to me.

Reading mentioned commit and the referenced internet page, and 
carefully reading the code in main.qml I find 2 opacity related pieces 
of code commented out (by Tomaz), telling "ApplicationWindow has no 
Opacity calls no more." (commit 4db80aa1a404dc). Hmm, weird. I just 
looked at the Qt docs: opacity on ApplicationWindow is a property since 
Qt 5.1, Tomaz: there is probably something I do not understand, but can 
you explain that commit?

I enabled that opacity code again. No visible effect, so I change the 
fade-in animation to 10 sec (yes ridiculous long, but ease to spot while 
running the app). No visible fade in anywhere. Question for Dirk: as 
original author, have you ever seen that fade in?

The referenced internet page (from commit 04e994b57558ed9), also 
explains that there needs to be a QML Loader object, and we do not have 
one. (So, I believe there was never a fade-in animation). I added one 
... and suddenly ... I have a nice 10 seconds opacity fade-in of the app 
:-) That is: on desktop.

And now it gets even more confusing. Running this changed code on 
Android, results in numerous (probably 10000 (milliseconds)) error 
strings in the log: "This plugin does not support setting window 
opacity". So, a piece of Qt code is called that is not implemented for 
Android. But ... the current app has some transparency features, for 
example the toast notifications. So where is that coming from? Anybody 
knows?

--jan