Add Fit To Height zooming and shortcut

Added Fit to Height option in zoom drop-down, and ability to shortcut
via "Configure Krita..." Set ZOOM_HEIGHT enum value to 16,
so ZOOM_HEIGHT is a unique mask in KoZoomController::Private
(see KoZoomController_p.h line 41)

This commit resolves: https://bugs.kde.org/show_bug.cgi?id=410929

BUG:410929