OPENDJ-1308 Migrate schema support


Transformed ExtensibleIndexer's getKeys() into createKeys(), using ByteString instead of AttributeValue and byte[].


ExtensibleIndexer.java:
Transformed getKeys() into createKeys(), all implementations have been updated.
Removed the createKeys() empty implementation that overrides the interface declaration.

ApproximateIndexer.java, OrderingIndexer.java, SubstringIndexer.java:
Consequence of the change to ExtensibleIndexer.
Removed the now unused logger.

EqualityIndexer.java
Consequence of the change to ExtensibleIndexer.
Added equalityRule field + passed it in the ctor, to cater for the fact we do not use AttributeValue.getNormalizedValue() anymore.
Removed the now unused logger.

TestBackendImpl.java:
Consequence of changing 

CollationMatchingRuleFactory.java:
Consequence of the change to ExtensibleIndexer.
Extracted method createRangeMatchQuery().

TimeBasedMatchingRuleFactory.java:
Consequence of the change to ExtensibleIndexer.
Extracted method addKeyIfNotZero().

AttributeIndex.java
JEExtensibleIndexer.java