Allow to disable some emoticons

Talked about this with vmassol on irc: there is currently no way to disable an emoticon in xwiki (it's possible to disable all of them or to add a new one).

In our case, we have a lot of wiki pages that were created by copy/pasting documentation with a lot of

(n)

. It would be nice if we could disable this specific emoticon in this case.

Creating this issue as trivial because there exists other way to handle this with http://snippets.xwiki.org/xwiki/bin/view/Extension/Replace%20Word%20Snippet for example.