Discuss bundling filebeat and beats-input into one gem - to replace the file-input.

Some ideas to explore (PH and I discussed this v. briefly in Prague):
- The filebeat and the beats input would run on the same machine and not on the edge.
- Logstash would control the filebeat lifecycle (similar to prelert integration if and when).
- Logstash will supply the beats config by translating the file-input user config initially but allow for the filebeat config to be specified directly in the user config with some keys in the `logstash.yml` if it made sense.
- The filebeat executable would ship with the gem.
- The docs for such a dual tech input would be filebeat + beats input docs merge plus clean up.
- Support would more easily support just one setup.
- Our local testing would give us more real world coverage.

/cc @ruflin