Remove hierachy-changed signal handlers when not needed

[godiard]

Fixing OLPC #10930 we found the ToolButton has a signal handler for hierachy-changed because need set the accelerator when is attached to a activity. But the new toolbar parent and unparent the page every time is displayed/hidden.

We can remove the signal handler once the accelerator is set, but need check the case when the accelerator is changed (like in Terminal)

In the activities logs appear many times"WARNING root: No gtk.AccelGroup in the top level window." after fixing it we can remove the log, because is not useful. Or think a more efficient way of resolve this.