Import erc-bbdb.el, erc-chess.el, erc-nicklist.el, and erc-speak.el

Import erc-bbdb.el, erc-chess.el, erc-nicklist.el, and erc-speak.el

* lisp/erc/erc-bbdb.el, lisp/erc/erc-chess.el,
lisp/erc/erc-nicklist.el, lisp/erc/erc-speak.el: Import these files
from commit 9497cc92bf1feb63c24425c46b1e033265c2cea9 of
https://git.savannah.gnu.org/cgit/erc.git, the old ERC repository
outside the GNU Emacs source tree.  These FSF-copyrighted files were
part of ERC before erc.git was (for the most part) folded into
emacs.git, but they were left out largely due to depending on packages
outside Emacs.  It is worth noting that their dependencies are all
free software, and bbdb and chess are actually available on GNU ELPA.