this fixes the bug in flake, where single key shortcuts prevented text input.

to reproduce, do the following:
1. open shortcuts configuration and assign the shortcut "a" to the about dialogue.
2. activate default tool => a shows about dialogue
3. create textshape and write something with a => about dialogue shows, but it shouldn't

In the qt lib textinputs are working, while there are these shortcuts, so in flake it should also work.

the patch works this way:
the canvas forwards bool QWidget::event(QEvent* theEvent) to KoToolProxy. The tool proxy asks the current tool, if it is in text mode (isInTextMode) and interrupts the shortcut if so.