View whole file at once in PR

Issue:  Users prefer being able to open up an entire file to see all of the code context above and below the diffs rendered in the PR. The new experience doesn't offer.  

Proposal: Make it possible for users to trigger a modal that shows the single file in its entirety (up to a certain limit) in either SBS or unified diff mode, along with the comments present on the code itself.

Designed Solution: 

1. How to trigger

2. The Modal View

3. Error State if File is Too Large (temporary solution)