Disable 'click anywhere to punch clock'

That turned out to be a problem when, for example, clicking the window
just to give the page focus resulted in a punch.  Turns out, a clock
punch is a bit sensitive to false positives.

[amend]: Change the instructions box to indicate this change in
interface.

Also removed 'timeclock.html', the original name for index.html.
Merge branch 'master' of https://github.com/borkabrak/timeclock