Fix toggle command contributions

State ID has to be RegistryToggleState.STATE_ID in order for HandlerUtil.toggleCommandState( event.getCommand() ) to work
Do not persist toggle state to workaround potential bug

Otherwise, the toggle state would be restored when restarting Eclipse but the
view would not notice that the synchronization is supposed to be active.
Update selection when activating editor synchronization

Now works just like in Package Explorer.
Synchronize icon

Source: http://wiki.eclipse.org/UI_Graphics_:_Design_:_Common_Elements
More distinctive refresh icon

Not to be confused with "editor synchronization" as easily anymore.