Change global Klipper shortcuts to use the Meta key by default

The current shortcuts could conceivably override app shortcuts, since
they don't use the Meta key. The following changes are made:

Automatic Action Popup Menu:                 Ctrl+Alt+X -> Meta+Ctrl+X
Manually Invoke Action on Current Clipboard: Ctrl+Alt+R -> Meta+Ctrl+R

These are safe to change in the code rather than adding a new one and
keeping the old ones around for compatibility's sake because
KGlobalAccel::setGlobalShortcut by default preserves old shortcuts
when they are changed, and we aren't overriding that behavior here. So
only new installs will get the new shortcuts and existing user installs
will be untouched.