Underline is hidden by background shape

[afester]

With the following CSS

-rtfx-background-color: #dcdcdc;
-rtfx-underline-color: blue;
-rtfx-underline-width: 1px;

the blue underline is hidden by the gray background shape.
The underline should be in front of the background shape instead. The following hack in ParagraphText.java fixes this:

getChildren().add(/*0,*/ underlineShape);

by adding the underline shapes to the end of the ParagraphText's child list. Needs some additional verification before submitting a pull request.

[TomasMikula]

Fixed by #408