Fix AE2 grid node connection issues

* When breaking a CM with AE cables connected to it, the gridnodes
  never got correctly destroyed leaving "ghost" connections visible
  to the player.
  This is fixed by destroying the node when the tileentity invalidates.
  See the todo below for more information on where this introduces a bug.
* When placing down an entangled CM or when entangling a compact machine
  the surrounding AE blocks will get notified and connect accordingly.
* Do not connect AE as long as the room has not been used before. This
  prevented the real gridnodes from connecting properly.

For bugs introduced with this please read issue #68

This should fix all or some of #60, #65 and #66: please retest.
Other issues probably relate to the newly created issue with above
todo.