Unify DocumentedException and RestconfDocumentedException

YANGTOOLS-1303 has introduced a set of yang-common constructs which model the details carried in these two exceptions.

 Eliminate duplication between netconf-api and restconf-common, so that maximum number of yang-common constructs are used.

Note that some constructs may need integration with yang-data-api, but at the end of the day, both these exceptions should just implement o.o.y.yang.common.YangNetconfErrorAware, allowing them to be seamlessly bridged.