Various ERC customizations

* lisp/bandali-erc.el: Make 'erc-pal-face more subtle, with a slight
yellow background.  Also, set erc-pal-highlight-type to the
newly-added `message' type [1: e365b9ab7b], which in contrast to
`all', only highlights the message body and not the nick.  Lastly, add
the tilde.chat network.

[1: e365b9ab7b]: 2020-08-14 22:12:02 -0400
  Add `message' to erc-match.el highlight types
  https://git.savannah.gnu.org/cgit/emacs.git/commit/?id=e365b9ab7b989c0587c0f2c0f05d35b4d67920dd