Got rid of internal status

The status is stored in the GSettings key; there is no reason
to store the status in the extension too. That way the extension
will recover from external manipulation of the state.
Fix "extension stop working after a screen lock" bug.

It seems that the button.connect() call has to be made in
the init() callback and not in the enable().
Refactoring the sync thing
Merge branch 'stateless'

Conflicts:
	SwitchFocusType@romano.rgtti.com/extension.js -- fixed
Bump version number to 4.