Support comments in the side-by-side diff view

Users request the ability to view, create, and edit comments in side by side mode. 

Proposed Solution: 

We're going to do the following to make this work: 

1. Limit comment nesting to one-level to prevent comments from getting too horizontally squished in long conversations. 
2. Fix a previously mentioned horizontal scrolling problem with side-by-side mode by wrapping code 
3. Make it possible to view, add, edit, and delete comments. 

Design: