HTML5 Text updates 

The current HTML5 support for text properties is incomplete and broken.  This patch corrects the object reference (from impl to canvasContext) for textAlign, and adds support for textBaseline.

Note that there is a problem with HTML5Canvas.ie6.py - as distributed, an app using HTML5Canvas fails to complile with a missing LinearGradientIE6 reference - however, renaming this file to .pyq allows the build to complete and the apps work fine.  I don't understand the override system well enough to fix it :-(     and IE6 is a pretty pointless target in this case anyway.