Support tracking URLs with tokens in query strings

URLs with tokens in mailings do not have click tracking. This is an important metric for fundraising (e.g. to see how many and even which contacts click through to contribution pages). @artfulrobot put together some code that worked well to track these clicks in Flexmailer, but that code was not merged before Flexmailer was merged into core.

https://github.com/civicrm/org.civicrm.flexmailer/issues/30

We used this without issue for four months and found it worked very well. @artfulrobot was using it since March. Would it be possible to merge this into core. Rich, would you be willing to copy your code to a patch against core?