Propagate upstream coluring labels to target issues when rendering target-only view

[str4d]

The "target issues" view excludes interstitial issues to give a high-level view of what is being worked towards. We should merge the state of those excluded issues into their relevant downstream target. For example, if an issue directly upstream of a target is in progress, the target issue should be rendered blue in the target-only view (but not the regular view when the in-progress issue is visible).