Support displaying sub-jobs of multibranch pipeline jobs.

[emmanuelthome]

Hi. Could you please consider this pull request ? This is an attempt at some new functionality. Works for me. Sub-jobs are listed as (parent job)/(branch name) in the drop-down indicator list.

[emmanuelthome]

Doh, there are already pull requests for that functionality. In contrast to other proposals, I'm not using the depth field of the json api. Using even depth=1 has the drawback of exposing all occurrences of the top-level builds in the json response (in my case, this aggregates to several thousands).

Instead, I'm doing ancillary queries to find the branches of the multibranch jobs.

Not saying either approach is better, please do as (and when) you see fit.