Move constants from oak.query.QueryImpl to oak.spi.query.QueryConstants

in the light of the modularisation effort i had a look at the query code and noticed that the constants defined on QueryImpl are needed outside of the scope of the query implementation.

IMO that indicates that those constants are of broader use and might better be located at oak.spi.query.QueryConstants. moving would in fact remove all imports of QueryImpl in the oak-lucene module.

tmueller, teofili, it will attach a proposed patch for this improvement and would appreciate if you could review if you are ok with that change.