Make action=mobileview GET, not POST.

* Android uses GET for action=mobileview. So too shall iOS.
* GET will make the traffic eligible for pageview counting.
* Future work: if necessary, make parameter order and signatures consistent across platforms.
* Future work: if necessary, make one of lead/remaining sections calls a POST to shield against double counting.
* Note: the pageview calculation may be mutable to (not) count certain action=mobileview signatures.

Change-Id: Ibf62c451f93eb00360f122ae1e1dcd8308f7d617