Change global 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:

Switch keyboard layout:               Ctrl+Alt+K   -> Meta+Alt+K
Activate window that wants attention: Ctrl+Alt+A   -> Meta+Ctrl+A
Kill Window:                          Ctrl+Alt+Esc -> Meta+Ctrl+Esc

These are safe to change in the code rather than adding new ones and
keeping the old ones around for compatibility's sake because
KGlobalAccel::setDefaultShortcuts 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.


(cherry picked from commit 529c3c29)