Add plugin version in es-plugin.properties

With https://github.com/elasticsearch/elasticsearch/issues/2784, we can now add plugin version in `es-plugin.properties` file.

It will only be used with elasticsearch 1.0.0 and upper. No need to push it in 1.x branch.

Closes #59.
Update to elasticsearch 1.0.0

Closes #57.
Support group id in addition to group names

Based on issue #43, we want to support both notations:

* group name first
* group id if it does not work with group name

Closes #49.
Elasticsearch dependency should be provided and not compile

Please change the Elasticsearch dependency to provided (and maybe testCompile) instead of compile and runtime.

Why? If you include the plugin in embedded Elasticsearch, and you exclude anything from the Elasticsearch dependency, it is undone by this dependency also including Elasticsearch. Therefore you have to tune both, when really this plugin only needs it as provided (since it runs with Elasticsearch or in Elasticsearch but never on its own).

Closes #48.
Support ap-northeast region for EC2 and S3

Closes #52.
Changed AwsS3Service to use one client per region and credentials combination and made S3Repository specify credentials if such exists in the repository settings. Updated readme with repository specific credentials settings.