Added option to remove rank/file labels

[JeffML]

Unfortunately there are code format changes, so I'll explain here:

1. added a boolean labels prop; if true, behavior is same as now
2. if false:
   1. the labels are not shown
   2. the board and pieces are shifted over (no left padding)
   3. the board size is adjusted (no right padding)
3. added an input control to the demo
   1. note that there is an existing bug for both flip (and now label) checkboxes : it will only re-render when checkbox is toggled twice
4. not fixed: the piece selection square is now off-by-one; I'm not using this and will probably not get around to fixing it
5. also added package.lock.json to repo
6. npm audit reveals lots of issues, but I did not try to fix