Focus RichTextArea by mouse.

[tonydroy]

Style a RichTextArea so that it looks like a TextField (with space for only one line). Compared to a real TextField, it is very difficult to focus by mouse click -- only certain very fine locations will work. This issue may be related to #154.

Addendum: I have been able to work around this by wrapping the RTA in an HBox, with a mouse filter on the HBox that requests focus on its RTA when the box gets a mouse pressed event.