Adding tagging at all topology levels

[vdogaru]

Currently, TStreams can be tagged when a topology is declared. Tags are inserted in the JSON graph representation, so the console can display tags associated with the graph elements, show streams by tag name, etc.

Application developers should have the ability to add tags at all topology levels. This requires a Tagable interface that may be implemented by children of TopologyElement:

public interface Tagable {
    /**
     * Adds the specified tags. Adding the same tag multiple times will not change 
     * the result beyond the initial application.
     * 
     * @param values  Tag values.
     */
    void tag(String... values);

    /**
     * Returns the set of tags associated with this instance.
     * 
     * @return set of tag values.
     */
    Set<String> getTags();
}

[vdogaru]

Issue moved to https://issues.apache.org/jira/browse/QUARKS-69