Fixes issue with role election in cluster

Introduces tests and fixes for some edge cases that role election
 may come up against
Votes received that are actually delayed responses from a previous
 election could lead to wrong results. This is now guarded against
 by having versions marking elections and vote requests/responses
Election results could be reordered if one would fail to be
 broadcasted. Now this is guarded against by an election epoch, allowing
 election results to be ignored.
Instance and vote count could become wrong if an instance voted
 and then was marked as failed before the election finished. That could
 lead to cases where the role holder was not asked for a vote. Now,
 ElectionContext registers as a HeartbeatListener and will invalidate
 votes of instances that have failed.
This is added with backwards compatibility, so elections initiated by
 previous version instances will still go through and receive proper
 responses.
Logging performance optimizations:
* Added custom Jetty logger that caches isDebugEnabled
* Changed LogbackService to cache isDebugEnabled
* Added isDebugEnabled check before toString() in HighPerformanceCache
Only add security filter if there are security rules
License header fix
Debug cache is now no longer static.
Added comment that the request log needs to decorate all other handlers.
Added test for slave-only instance being elected coordinator
Fixes so that slave-only instances not only try not to win elections, but actively don't switch to master in the case they are coordinators (e.g. because the instance created the cluster)

Conflicts:
	enterprise/ha/src/main/java/org/neo4j/kernel/ha/HighlyAvailableGraphDatabase.java
	enterprise/ha/src/test/java/org/neo4j/ha/TestSlaveOnlyCluster.java
2.0.3 changelogs
Merge pull request #2339 from jakewins/1.9-merge

1.9 merge
Tagging for version 2.0.3
Handle pruning old format logs, Fixes #2265
Handle backup when no logs are present on target db.
Added +UNWIND+ to Cypher

UNWIND can be used to transform a collection into individual rows.
Back to development version.
Minor changes to UNWIND

o Added more a few more tests for edge cases
o UNWIND now does not remove anything from scope,
  only adds a new identifier for the elements
o Tweaked the documentation
Add UNWIND to shell
Update version numbers for 2.0.3 release.
Merge pull request #2345 from benbc/2.0-update-to-2.0.4

Update version numbers for 2.0.3 release.
Logging performance optimizations:
* Fixed custom Jetty logger to caches isDebugEnabled
* Changed LogbackService to cache isDebugEnabled
* Added isDebugEnabled check before toString() in GCResistantCache

Only add security filter if there are security rules
Merge pull request #2331 from jakewins/2.0-backup-with-no-logs

Handle backup when no logs are present on target db.