Support custom labels and annotations for Deployments/StatefulSets

[lovetoburnswhen]

Allow users to configure additional labels and/or annotations on the Deployment/StatefulSet objects (not just for pods/services). This feature would be tremendously useful for environments that require certain labels to be set - currently the only alternative is to maintain a fork of the chart internally, which seems quite wasteful just to add a label.

[lovetoburnswhen]

#666 and #667 add resource-specific keys whereas #668 extends the common labels. @rawkode @gitirabassi @timhallinflux let me know if you prefer one of these approaches and I can make the requisite changes.