Add some additional shortcuts for actions

Add Cmd+Shift+- for decreasing font size on macOS.
Do not add Cmd+= for increasing size, because it conflicts with the
existing shortcut for "Replace and Find Next".

Sprinkle some Backspace shortcuts in addition to Delete for removing
items. There are (laptop) keyboards that either do not have a designated
Delete key (requiring Fn+Backspace) or where the Delete key is not
conveniently located/sized, and there is no benefit in making the
distinction in that case anyhow.

Fixes: QTCREATORBUG-706
Fixes: QTCREATORBUG-13733
Change-Id: I06274a9810b82800ec6158a883c95d2a7ae2465e
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/qmakeprojectmanager/customwidgetwizard/classlist.cpp

@@ -147,6 +147,7 @@ void ClassList::removeCurrentClass()
 void ClassList::keyPressEvent(QKeyEvent *event)
 {
     switch (event->key()) {
+    case Qt::Key_Backspace:
     case Qt::Key_Delete:
         removeCurrentClass();
         break;