Auto-populate the first value(s) for a custom series

[EricRahm]

In theory we should be able to figure out the closest parent of the first build in a custom series that's in the regular arweslimyet DB and add that as the first value in the graph. This would get rid of the need to push a baseline test prior to testing a set of patches.

The current methodology is usually:

1. push baseline build to try, request custom AWSY run
2. push patches to test on top of baseline to try, request custom AWSY run

But that could become:

1. push patches to test on top of baseline to try, request custom AWSY run

This could probably be done in the json building step for each custom db.