Only refresh id_cache if the parent field is active.
[SPEC,TEST,FIX] add spec and tests for termvector api and fix inconsistencies

- index and type were not read from the uri with the _mtermvectors api
- ids were not read from the uri parameters with the _mtermvectors api
Deprecated use of partial fields in Java API, was already deprecated in the docs for the search API

Closes #4118
[DOCS] Added multi fields link to mapping page.
Deprecated ToXContent.Params#paramAsBooleanOptional in favour of paramAsBoolean

Closes #4817