Added 'click' listener to put focus on the link item below.

I like the 'focus' best because it 'highlights' (sort of) the link and scrolls
to it at the same time. There are still a couple of issues:
- The dotted frame is invisible unless I hit <tab> a couple of times on the
  page.
- After this the stupid line is faintly drawn so I HAVE to use css.
- I implemented a checkbox to disable the dynamic list but deleted it right
  away - for it was coded horribly. But to remind myself that I can do better,
  the checkbox is still in place (incapacitated).
This highlights links if given focus by 'click' callback.
Implemented text field fo polygon count and buttons.

The buttons are labeled 'decrease' and 'increase' but they certainly DO NOT
JUST INCREASE THE POLYGON COUNT BY ONE!!! BECAUSE NOBODY WANTS TO CLICK TEN
TIMES TO GET FROM 12 TO 22 JESUS CHRIST. Increase sets a limit of e.g. 22 to
50, then 100, 200 etc.
The implementation of both buttons looks fairly unelegant but I don't see how
to do this with less lines of code. They look similar but nevertheless differ
enough to remain separated.
Labels are also misleading because the field should say 'object count' or
something.
Rewrite statement block as lambda in _list/tabulate.

I noticed this when I was working on the Douglas-Peucker implementation: the
ability to jump to the end of the block with some meaningful result enables me
to express this more concisely. Even with the arguably obfuscated closure, I
rid a bunch of verbose statements that have been there solely to say "ignore
this next block but still do the doc={}".