Fix scrolling direction in SongEditor due to stuck Ctrl/Shift.

[Cyp]

As far as I can tell, MainWindow::focusOutEvent never gets called no matter what I do, so clearKeyModifiers fails to be called.

[Cyp]

/home/travis/build/LMMS/lmms/include/MainWindow.h:130:22: error: ‘deprecated’ attribute directive ignored [-Werror=attributes]
Should probably be compiled with -Wno-attributes with old compilers.

[JohannesLorenz]

A bit more info please: What is the issue you are fixing? What are the steps to reproduce that issue?
Edit: This info should also be in the commit message.

[JohannesLorenz]

Not required but it will help future readers if you split stuff into multiple commits, e.g. cleanups, override fixes, ... It's not difficult, just a git reset --soft HEAD~1, and then git add on the files you want to add (or git add -p if a file shall be splitted).

[Cyp]

It fixes that if scrolling with the mouse wheel in the Song Editor, it would often unexpectedly zoom or scroll horizontally instead of scrolling vertically, due to a stuck Ctrl/Shift state.

This was reproducible by switching away from LMMS using Ctrl+F[1-10] to change desktops, and switching back again without using Ctrl. Then LMMS would behave as if the Ctrl key was still down. Not sure how to reproduce Shift being stuck down, but it also happened sometimes somehow.

As a side effect, it should also fix a theoretical issue of it thinking Ctrl/Shift was down during the click when it was actually pressed after the click (might happen in the case of very slow computers).

[JohannesLorenz]

Testing worked. Code and style are OK. Only left 1 comment about .gitignore.

[JohannesLorenz]

I also tested the ctrl key issue, it's working. No regressions for shift and ctrl. Testing finished.

[JohannesLorenz]

Thanks!

[PhysSong]

FYI, I'm getting a deprecation warning since Knob::getValue() uses deprecated MainWindow::isShiftPressed(). It will break CircleCI builds on master branch.

[JohannesLorenz]

I removed [[deprecated]] now on stable-1.2. Hopefully, this will fix the CI issues on master.