bug#24197: Removing lisp/play from standard Emacs package

[Otso Rajala <ojrajala@gmail.com>]

Emacs is primarily used as a text editor. Toys shipped in lisp/play directory
are fun, no question about that. Do they belong into core disribution of Emacs
is another question.

Problems:
1) They increase package size.
2) Their existence clutters M-x <tab> autocomplete lists: example M-x bu <tab>
has all things buffer, but also shows bubbles and butterfly, hardly useful
during editing process.
3) Tools > Games is a bit confusing: games are not tools by definition.
4) Help > Psychotherapist is toy in documentation menu.

Solution:
1) Make these toys in lisp/play optionally available from
elpa.gnu.org/packages, but do not ship them by default within
Emacs.

Advantage of solution:
1) All problems go away
2) Simple lisp game sources now easily accessible right from common browser
for fun & inspiration without having to download 56M tar.gz editor with them.
3) Fair towards other toys, considering sokoban and wpuzzle are there but don't
ship by default.

- Otso