Support for Part of Speech tags counting

[fdartayre]

Hi Alexander. Please have a look on the following pull request.

It contains:

• A new processor that uses OpenNLP POS tagger to count the different part of speech tags (the named entity recognition processor was renamed to avoid confusion between the two processors of the plugin)
• Upgrade to Elasticsearch 5.6.1
• Compatibility with Gradle 4.x
• Updated tests and README.md

[yehosef]

+1 - this would be great!

[spinscale]

I upgraded to ES 6.0 in the meantime... any chance for a rebase?

[fdartayre]

I will have a look on upgrading to ES 6.x as soon as possible

[ninesalt]

If this is still wanted, I added POS support in my fork for v6.5.4. I probably could have saved a lot of time by checking this PR and modified @fdartayre's fork before I forked the repo and added support for POS myself. Apart from the difference in versions, my fork counts the occurence of specific words as well. For example:

      "NNS": {
          "times": 1,
          "players": 3,
          "points": 1
      }, 

[spinscale]

@ninesalt feel free to open a PR!

[spinscale]

unfortunately this cannot be merged anymore. I do not have time to work on this. I will close this for now and hope someone opens a new PR.