Alternative splash screen status message implementation

[Wallacoloo]

This is an alternative implementation of #1915 that avoids using signals/slots or deriving from QObject.

It implements a new Messenger class that might be useful in removing core -> gui dependencies elsewhere too.

[curlymorphic]

This all works :)
@Wallacoloo thanks for this.

might be useful in removing core -> gui dependencies elsewhere too.

Justs a side note, I know there are future plans for RT-safety in the audio core. So this message system may not be suitable for use inside the audio processing code. I feel It is totally fine for it's current use :).

[tresf]

I really like this. We should get review by a few more core developers prior to merging. @lukas-w @diizy

[lukas-w]

While a message system like this is cool, it's overkill for just the splash screen. Also, Qt already provides a good debugging/logging system. See Qt's Debugging Techniques.
I think there's no need to bloat our code with this, so I'd strongly favor #1915.

[Wallacoloo]

@lukas-w thanks for taking the time to review this.

[Wallacoloo]

Closing, as this doesn't seem to be a preferred alternative & Lukas raised a good point about bloat.