Renamed $render* to $show* variables, del dbg flag

* Renamed all $renderXXX variables to $showXXX
* Removed unused debug flag renderZeroRatedLandingPage (can be simulated with headers)
* Cleaned up README obsolete flags

Change-Id: I7c8399c3f693d8df02aade08008aac32b6f6dcd6
Merge "Renamed $render* to $show* variables, del dbg flag"