DATACMNS-810 - Add core types for Query by Example support.

Added required types for Query by Example which should be used by the individual store implementations. 

Generally the Example type captures a sample object and allow various settings concerning the mapping into an actual query. So there’s configuration options for handling null values, string matching, property paths to ignore,

Related tickets: DATAJPA-218, DATAMONGO-1245.
Original pull request: #153.

Author: christophstrobl