fix erc-highlight-nicknames being clobbered

I found the culprit that removed the nick specific coloring done by erc-highlight-nicknames.el, and commented it out.

While going through the erc-settings I also found that the inheritance in erc-error-face was not being applied properly, leaving the default red. For now I put in the specification for font-lock-warning-face explicitly which works.

I also added slightly more difference between erc-timestamp-face and erc-notice-face, since before you could not tell them apart.