Add invisible presence state

Please review, commit to internal build and allow some baking in the team.

Login screen is a bit squeezed now (i mean the animated logo). There is a gap between bottom buttons and Log in as invisible checkbox. Maybe this gap should be used instead of squeezing the logo. The width and height also got squeezed.. http://www.wroot.lt/jive/spark_588vs589.jpg

UPD: well it is only a visual effect that its width has changed.

Yes, you are right, we changed only the height of LoginPanel from 200 to 250. By adding a new checkbox we thought to keep the gaps.
I can ask Slava to revert it back if you want. Here is the change:

public Dimension getPreferredSize() {
final Dimension dim = super.getPreferredSize();

• dim.height = 200;
  + dim.height = 250;
  return dim;
  }

What about making it 230 or 240, so it won't be such a big blank gap?

Sure, I agree, I will change it to 230