Migrate (or redirect) "Tokens" wiki page

Created by: seancolsen

I noticed this wiki page: https://wiki.civicrm.org/confluence/display/CRMDOC/Tokens

Which is referenced right above this heading: https://docs.civicrm.org/dev/en/latest/framework/civimail/#html-vs-text

@seamuslee001 you did some work to bring in docs on tokens. Did you import this page? If so, let's redirect it. If not, let's see if there's useful content in there which we can bring over.

Once we've done that, let's replace the wiki link with an internal link.