(CXF-6148) Added a basic support of xsd:choice elements in JS generator.

This fix adds a basic support for xsd:choice elements.
There are several limitations:
* JS does not check xsd:choice restrictions (it is currently possible to set several xsd:choice members at the same time, but this should eventually result in SOAP BE error)
* xsd:choice with maxOccurs > 1 still not support
* xsd:any inside xsd:choice is not supported as well

Covered it with tests and did small improvement to the tests.
Also added log message when not supported exception is raisen, since it was not enabled previously.