Modal window improvements

1. Currently the modal window is located at the top of the screen. We would prefer putting it in the center of the screen. The animation time can be eliminated or reduced and could come out of the center.

2. We have a request that the user can move the modal window: she wants to be able to see underlying figures sometimes.

3. The user has to click twice on the OK button in order to invoke the modal window.

4. Make pressing the enter key invoke the OK action.