composer allows creation of graphs with un-removable metrics

[Dave Rawks]

In the composer if you add two identical metric lines in the "graph data" window they will be deduplicated into a single item in that window's display. If you then select the metric and use the "remove" button the metric name is removed from the "graph data" window but the metric is still present in the graph window. Similarly if you have 2 data sources and one is a metric name and the other is the same metric name but with a function applied to it; if you use the "undo function" against the metric with the function applied the line will disappear from the window and the same un-removable behavior will be exhibited.

[Michael Leinartas (mleinartas)]

The issue is that the new target is always added to Composer.url (used to actually render the graph) but is only conditionally added to the TargetStore ArrayStore which drives the graph data window.

I'm going to remove the restriction that no duplicates are in the Graph Data window as I feel it's a valid use case for a composer. A user may add a duplicate (or end up with a duplicate) while applying and undoing functions while composing a graph, even if a duplicate is not the intended final result.

[Michael Leinartas (mleinartas)]

Committed in r763