1. Fix auto-flipping of styles
The StyleRegistry didn't account for LTR/RTL when caching the results of
style resolution. The 'writingDirection' style is no longer flipped; no
clear use case for it.
2. Remove experimental '$noI18n' style prop suffix
This feature is essentially unused, and less likely to be used with the
introduction of 'dir=auto' on 'Text'. Removing also marginally improves
render performance.
Adds support for opening external URLs in a new tab/window. Includes
patches to 'Text' to improve accessibility and 'createDOMElement' to
improve external link security.
Fix#198
