Canvas MessageBox: make sizeable / newline support
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Hi,
i wanted to show a nice welcome message at the C182 and stumbled upon a problem with the MessageBox implementation. It always has a fixed size.
It would be cool if the messageBox could be sized optionally, so I added a small patch introducing an optional parameter.
PR hereby:
* Repo https://beni.hallinger.org/git/fgdata.git
* branch `CanvasMessageBox_sizeable`
If its merged I will ammend the wiki page: https://wiki.flightgear.org/Canvas_MessageBox
-----
```
# Examples:
canvas.MessageBox.information("Orignal", "bla bla bla", nil, canvas.MessageBox.Ok);
canvas.MessageBox.question("Bigger", "BarContent", nil, canvas.MessageBox.Cancel, [300, 300]);
```
issue