Pull request to set max zoom

[GoogleCodeExporter]

Not sure how to do a pull request ala GitHub, so I'm filing as an issue. This 
is a feature I added for my own benefit.  I added a new contextual menu item to 
PlayActivity to go to the maximum zoom level.  

The maximum zoom was a magic number of 2.5F, but on a phone my eyes need a 
greater magnification.  I did some refactoring of the literal float into a 
roughly calculated value in PlayboardRenderer.getDeviceMaxScale().

There is another instance of 2.5F in ScrollingImageView.maxScale, but I'm not 
certain how this value interacts with the one in RENDERER, so I left it alone.

Tested on XOOM, Nexus 7 and Nexus 5.

https://code.google.com/r/ehcloninger-shortyz/source/detail?r=cbfe4dda94698b03a8
8d970df41a59bb2ea9c1d8

hg put R.Java in the commit, but it's clearly not needed.

Original issue reported on code.google.com by ehclonin...@gmail.com on 3 Mar 2014 at 3:20