Improved sorting/grouping performance

* Pulled expensive operations while retrieving context out of inner loop
* Made cid and fiid fields numeric, stored and indexed for caching
* Used field cache to speed up getting fiid
Fixed "too many hits" message showing in error
Added containing, within, starts at, ends at support.

* SpanQueryPosFilter (renamed from SpanQueryContaining) handled all
these positional-filtering cases
* SpanQueryTags, DocIndexerPageXml updated to new way of indexing XML
tags (end tag at preceding token instead of next)
* Above features added to CorpusQL parser
* SpanQueryNot now also has field name when it is used as a matchall