Minor correction (element focus)

If the user doesn't input a message and clicks 'Send,' nothing was done,
which is the expected behavior, but the focus remained on the Send
button.  Now focus is given back to the text input box, in order to
simplify user input.
Added (missing) board image.

I was referencing the board image in the CSS file, but for some reason
that goes beyonf me, I was not tracking the image.  So I incorrectly
pushed my commits without the board image but with a reference to it in
the CSS file.  (Shame on me, I know!)

This commit corrects that mistake.