[SplashScreen] use directly QSplashScreen & update splash medInria logo

[mathildemerle]

As done on MUSICardio side: Inria-Asclepios#800

This PR removes the use of medSplashScreen which is not needed anymore, we can use directly QSplashScreen.

It's now launched at the creation of the app (in the beginning of medApplication constructor), and automatically closed when the window of the app is displayed.

This change debugs also a problem at least of Ubuntu side where the splashScreen was not displayed at the right time.

Also, i updated the medInria splashscreen logo to be a dedicated one (not the same as the one on homepage), with a background color, and no need to space for text.

Ⓜ️

[Florent2305]

At a moment of code review the question was

QSplashScreen *splashScreen

leek or not ?

Thanks to Mathilde investigation, the lines

d->splashScreen->setAttribute(Qt::WA_DeleteOnClose, true);

d->splashScreen->finish(d->mainWindow);

prouve we don't have a leek.

Then for me the PR is good to merge ;)

But a question still open. After the line

d->splashScreen->finish(d->mainWindow);

Do we need a d->splashScreen = nullptr; the answer to this question is in a future discussion...

[Florent2305]

Ok

[mathildemerle]

as a reminder it's possible to switch QSplashScreen *splashScreen; to QPointer<QSplashScreen> splashScreen; because QPointer set automatically to null the variable if it has been deleted. It's not really useful here but could be helpful in other part of the code