#2930 Review rework for #2931.

- Set an explicit timeout on WebFilterSessionCleanupTest
- Corrected Checkstyle errors in SessionListener and WebFilter
  - Split WebFilter.createNewSession into multiple methods to reduce
    its complexity
- Added more class-level and package-level documentation
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# On branch 2930-bturner-reference-count-sessions
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# Changes to be committed:
#	modified:   src/main/java/com/hazelcast/web/SessionListener.java
#	modified:   src/main/java/com/hazelcast/web/WebFilter.java
#	modified:   src/main/java/com/hazelcast/web/package-info.java
#	modified:   src/test/java/com/hazelcast/wm/test/WebFilterSessionCleanupTest.java
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