Added ingest wide template infrastructure to IngestDocument
Added a TemplateService interface that the ingest framework uses
Added a TemplateService implementation that the ingest plugin provides that delegates to the ES' script service
Cut SetProcessor over to use the template infrastructure for the `field` and `value` settings.
Removed the MetaDataProcessor
Removed dependency on mustache library
Added qa ingest mustache rest test so that the ingest and mustache integration can be tested.
Martijn van Groningen