Add v and u to params sent to `before_beacon`
Add v and u to params sent to `before_beacon`

`before_beacon` handlers should get access to all parameters that will
be added to the beacon url.  This includes the boomerang version and url
of the page (even though all handlers could just get this out of the
global space).

This of course means that we can no longer assume that v and u will be
the first two boomerang added parameters on the beacon.

Ref: Issue #1 and Issue #4

FredXue/boomerang,levexis/boomerang,forcedotcom/kylie,forcedotcom/kylie,sdgdsffdsfff/boomerang,lognormal/boomerang,FredXue/boomerang,lognormal/boomerang,levexis/boomerang,sdgdsffdsfff/boomerang