Add Feature Completions and Remote Kills to Split details screen

[samandmoore]

Summary

Since we added "remote kills" and "feature completions" to the TestTrack feature set, we have not updated the Admin UI to display them. This PR adds both of these features as tables on the split details screen.

feature gate with feature completion and remote kill

feature gate with no completions

experiments don't use feature completions

experiment with no completions and no remote kills

Other Information

I also upgraded to mini_racer because i couldn't run the app locally otherwise.

/domain @Betterment/test_track_core /no-platform

[nanda-prbot]

Needs somebody from @Betterment/test_track_core to claim domain review

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[nanda-prbot]

@samandmoore needs to incorporate feedback from @aburgel. Bump when done.

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[jmileham]

One comment on wording

[samandmoore]

bump!

i ended up having to sneak some rails 5.2 stuff in here because the app was not working properly locally without those changes. there's still some funkiness with auto-loading, but we can figure that out separately

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[samandmoore]

bump @aburgel

i'm just trying to determine if we can remove some of the environments/ files

[samandmoore]

i'm just trying to determine if we can remove some of the environments/ files

determined! and deleted.

[aburgel]

domainlgtm!

looks like travis is choking on the ruby 2.4 build. i'd say it's time to retire that version.