Removed contentsField instance var. from Indexer class.
HitProperty classes now take fieldName and propertyName separately.

If you constructed a HitProperty class using a combined (Lucene)
field name, such as "contents__lemma", you should change to using the
new constructor with the separate property parameter.
In new index naming scheme, main property now has a name (e.g.
"word").

- Changed variable names to make the types of (partial) field names
clearer.
- Updated indexers to correctly connect the default forward index to the
main property instead of the whole field.
- CorpusQL parser now correctly uses defaultProperty set by client.
- IndexStructure now detects main contents field and main property for
each complex field.