Implement stateful support for master node (resolves #15)

[clockworksoul]

This change implements stateful support for master nodes as requested in issue https://github.com/clockworksoul/helm-elasticsearch/issues/15.

Changes include:

• .Values.data.stateful.enabled and .Values.data.stateful.class attributes have been moved to .Values.common.stateful
• templates/es-data.yaml logic has been adjusted to account for above point
• templates/es-master.yaml updated to include the same StatefulSet logic as templates/es-data.yaml
• Chart.yaml version bumped from 0.0.5 to 0.1.0. We don't have any defined rules around how out versioning will work, but the changes to values.yaml made a minor version bump seem appropriate.

NOTE: I set the default master node volume to 8Gi. Does this make sense? I'm not sure how much space the master node metadata requires even in large production systems, and I'd like the comments in the values file to describe that.

[sagikazarmark]

Side note: 12Gi is the default here: https://github.com/pires/kubernetes-elasticsearch-cluster/blob/master/stateful/es-data-stateful.yaml#L73

[clockworksoul]

12Gi is the default for the data nodes, but there isn't any stateful master in the pires project yet (once this is tested and demonstrated to work, I'll submit a PR there, too).

You make an excellent point regarding the possibility of people possibly taking the default as a recommendation. I try to comment robustly enough to make that clear, but in my experience most people (including me) don't read the comments until something breaks that they have to fix.

I'll set the master default to 2Gi and leave the data default at 12Gi.