Add `XCSSMatrix` library
Remove error in non-WebKit browsers. Required for testing in non-WK envs.
Use `XCSSMatrix` if `WebKitCSSMatrix` is not available.
Add the module to manage the prefixed CSS & JS properties.
First pass at unifying the approach to accessing JS & CSS properties.

 * `lookupCSS` and `lookupJS' accept the non-prefixed property name and returns the supported property name. Return values are either vendor-prefixed, not-prefixed, or `false` if it's unsupported
 * `lookupCSS` accepts a dashed CSS property value (like `box-sizing') and `lookupJS` accepts a camel case string (like `boxSizing`). It would be trivial to implement versions which accepted multiple argument types and returned the correct value, but punting on that until it's needed.
 * The lookup table (for both JS and CSS values) is generated at "compile-time" based on a list of values known to be used. The `lookup*` functions could be altered to do lazy loading if desired. That approach was avoid in this initial version to avoid any run-timeperformance penalty.
The z value is index 2, not 3.