Introduce ternary logic in Cypher

o Make Predicate return Option[Boolean] instead of Boolean
o Introduce isTrue that returns false for all cases except when the
   predicate returns Some(true)
o Add logic for IN, ANY, ALL, SINGLE and NONE to handle nulls
o Add a new section on working with nulls to the manual
Rename the GCR Cache to High-Performance Cache
Merge pull request #1476 from jakewins/rename-cache

Rename the GCR Cache to High-Performance Cache
Merge pull request #1458 from systay/ternary-logic

Introduce ternary logic in Cypher
Merge pull request #1465 from systay/merge-with-index

Fix problem when using MERGE and indexes exist
Proper cleanup on failed transaction commit in MasterImpl, added more logging.
Debug logging for channel.acquire in Client.java
Refactoring of optional match
Refactoring of MERGE
Allow MERGE to handle full patterns
Add documentation
Add documenntation for MERGE and patterns
in medias res
Refactoring of InsertingPipe in preparation for locking scheme for MERGE
Rewrite MergeConcurrencyIT
In medias res
Another in medias res