Configuring sensei purge filters
Support null in facet handler params
Support the purge filter
Small speedup to constructing term filters (reduce binary search space as we traverse.
Merge branch 'cnc-purge' into cnc

Conflicts:
	sensei-core/src/main/java/com/senseidb/conf/SenseiServerBuilder.java
	sensei-core/src/main/java/com/senseidb/search/node/SenseiHourglassFactory.java
	sensei-core/src/main/java/com/senseidb/search/req/SenseiRequestProtoSerializer.java
Fix transient test