Port to KGlobalAccel

Summary:
Port to KGlobalAccel. This enables us to drop khotkeys and display a configuration
dialog inside the application. The update script correctly sets the defaults and migrates
possibly user changed shortcuts. I didn't know where to place the KActionCollection
and put it in SpectacleConfig for the moment.

FEATURE: 388592
FIXED-IN: 19.08.0

Test Plan: Shortcuts should work as before.

Reviewers: #spectacle, davidedmundson, ngraham

Reviewed By: #spectacle, davidedmundson, ngraham

Subscribers: asturmlechner, ngraham, #spectacle

Tags: #spectacle

Maniphest Tasks: T10519

Differential Revision: https://phabricator.kde.org/D19310