Collapse parallel builds of similar name on Pipeline graph

Description

Pipelines with lots of parallel jobs that are all running the same basic command such as rspec 0 20 through rspec 19 20 should be collapsed to a single node on the pipeline graph.

This is continuation of https://gitlab.com/gitlab-org/gitlab-ce/issues/18141.

Proposal

• We will automatically collapse build names of this format: job-name {index} {total} or job-name {index}/{total} - e.g. /\s(\d+)[ \/](\d+)(\s|$)/ and replace with a single node; cutting the index and total.
• Use the worse status of all jobs.
• Add a drop-down for selecting individual jobs, sorted by our current convention (e.g. failed first).

Required work

• Backend to provide a list of builds grouped by similar name with the status including a list of builds
• Frontend to implement collapsing and showing a single entry, and having a clickable / hover-able option to show all collapsed builds

Links

• Should work seamlessly with official parallel jobs (#21480 (closed)), but could be implemented independently.