plugins/invert: Ignore key repeat in color inversion toggle shortcuts
Part of plasma-desktop#149.
This merge request prevents the toggle shortcuts in the Invert effect from constantly flashing the screen. This required making changes to kglobalaccel to facilitate detecting key repeat, but the benefit is being able to call QAction::setAutoRepeat(false) to ignore key repeat events in any effect where it makes sense to ignore them.
Related MRs:
Edited by Ritchie Frodomar