SolrDoc: An alternative whole-document search to SolrFull passage search

In whole-document search, the document title is suggested as an answer
generated by the "wholly-matching" document.

SolrDoc is not used yet by the main pipeline; for that, simply change
the SolrFullAnswerProducer reference in YodaQA.java to
SolrDocAnswerProducer.
AnswerMerger isLastBarrier: New parameter catering to parallel CAS multipliers
SolrDocPrimarySearch: Bump hitlist 6 -> 20

Processing these results is very cheap so we can be generous about them.
FixedParallelFlowController: New class executing independent CAS multipliers in parallel
YodaQA: Produce answers using both SolrFull and solrDoc

This brings together the last few changes and puts them into actual effect.