[80] Submission Detail Page

[stonefilipczak]

Adds a show page for individual submissions. Also adds the concept of comments to submissions so that a challenge manager can leave comments on a submission from this page.

This has consequential merge conflicts now because both the submissions details page (added in this PR) and the submissions list by challenge page are trying to live under the "show" namespace within the manage submissions route & controller.

I made an attempt to merge before I fully understood the problem and the result is the latest commit on this branch. If the last commit is rolled back you will see a fully working feature set but a bunch of merge conflicts.

I think we need to keep the show namespace for displaying details of a single submission and come up with something new for a list of submissions grouped by challenge. This is what "by_challenge_phase" was meant to solve earlier. Some of this confusion is because the manage_submissions/index page isn't a list of submissions, but a list of challenge phases. Maybe that page could exist in its own route and leave the manage_submissions/index namespace open for the list of submissions by challenge phase.

In scope:

• Submission details (referred to in the design as "Submission Materials")
• Comment form

Out of scope:

• Submission Eligibility for Evaluation Submission Eligibility for Evaluation (Prescreening) #81
• Submission Evaluation Details Submission Award / Advancement #84
• Submission Award Submission Award / Advancement #84