Config settings to disable index optimization/range calculation

Introducing two configuration parameters which allow users to disable
index optimization and range calculation during index cycling.
Also introducing configuration tunable which defines the maximum number
of segments during index optimization, defaulting to 1.

(cherry picked from commit 22e6800f31063e4973330c1603f3de7ff504459a)

Conflicts:
	graylog2-server/src/main/java/org/graylog2/Configuration.java
	graylog2-server/src/main/java/org/graylog2/indexer/Deflector.java
	graylog2-server/src/main/java/org/graylog2/indexer/indices/jobs/OptimizeIndexJob.java
Necessary changes due to cherry-picking.
Actual code for restricting index range calc to last one and deflector.

(cherry picked from commit 2f95dd29440999fca9ab0051865d690f3404e923)

Conflicts:
	graylog2-server/src/main/java/org/graylog2/bindings/ServerBindings.java
	graylog2-server/src/main/java/org/graylog2/indexer/Deflector.java
	graylog2-server/src/main/java/org/graylog2/indexer/ranges/RebuildIndexRangesJob.java
	graylog2-server/src/test/java/org/graylog2/indexer/DeflectorTest.java
Necessary changes due to cherry-picking.