Kibana 6.4.0 upgrade

[gmatheus]

Upgrading Comparable Time Range Plugin for Kibana 6.4.0.

Main changes:

• Project structure changed due to new Kibana Plugin Generator
• Private injector removed from some module imports (see Plugin API Changes in 6.4)
• Courier request handler decorator created (comparing request handler removed)
• Date histogram handler changed (see [6.4.0] Date histogram handler: empty buckets when splitting by terms #8)