UI: Click on Warehouse in DAG to select view of a specific Freightline

[rbreeze]

See comments here: #1156 (reply in thread)

[krancour]

Related to #1680

I will challenge the idea of "filtered view of Freightline" since that implies Freight from multiple warehouses being present in one single Freightline and I think we're sure we want multiple distinct Freightlines instead.

Clicking a Warehouse to select a Freightline (rather than filter) seems like a reasonable way of implementing a "Freightline picker."

Adding this to v0.6.0.

[krancour]

I think we would also need to change which specific Freightline is shown in response to clicks on Stages as well. Each Stage consumes Freight that originated from a specific Warehouse. When you start a promotion to a specific Stage or to all subscribers of a Stage, I believe we'd need to automatically update which Freightline we show so that it's populated with the relevant Freight for the Stage(s) in question.