Less annoying concept mouse-out behaviour

I'm trying to smooth out an annoying interaction in trying to rename a
concept. Before this commit, I would lose focus in the middle of
selecting the concept label because I would unconsciously click-n-drag
as though I were highlighting text, and in doing so would often bump
the mouse out of focus, which disables everything.

Now, once you click the text label, we ignore the mouse-out until you've
typed at least a character in the box
DEBUG: mechanism to display label for concept

Reality check
Slightly rephrase debugging labels
Tidy conceptdiagram css up a bit
Tweak to graphical tests notes
Slightly wider concepts
DEBUG: reenable renaming to see what's going on
Remove now unwanted generic debugging message