Size of navtable

I improve how the size of the navtable windows is calculated.

There are still some uses mostly with the width of the table in the center panel. The horizontal scroll bar is never shown.

Some more tricks can be tested to show the horizontal scroll but i think that this is not a priority:

* http://stackoverflow.com/questions/15499255/jtable-with-autoresize-horizontal-scrolling-and-shrinkable-first-column
* http://stackoverflow.com/questions/15234691/enabling-auto-resize-of-jtable-only-if-it-fit-viewport/15240806#15240806
* http://stackoverflow.com/questions/13213645/set-size-of-jtable-in-jscrollpane-and-in-jpanel-with-the-size-of-the-jframe

Let me now if more work should be done before integrate this pull request.