WMTS Support addition

Contribution for WMTS 1.0.0 support in cesium JS.

The spec.js file (Specs/Scene/WMTSImageryProviderSpec.js ) still needs to be substantially filled.
Some tutorials or examples of use should also be added.
Listed default is not correct.  Also I'm not sure that crediting OGC by default makes sense.  Maybe just don't have a credit by default.