Redesign the Diff UI for a more "warm and shiny" off the shelf experience

Problem/Motivation

The Diff UI can look somewhat cold and spartan with some themes.

This may be a bit of an extreme example, but this is the "off the shelf" experience with a custom theme that I work with:

Proposed resolution

Provide an optional, more opinionated design that provides a warmer, and more inviting experience for non-technical users.

• Use more user-friendly terminology, i.e. rather than "revision log message", simply use "notes" instead.
• Get the plugin settings out of the way by default to make the UI feel more minimalist and distraction-free.
• Display user avatars when available to provide a warmer feel. (Obviously, degrade based on permissions, site builder preference, etc.)

• Give the layout a facelift, overall

Remaining tasks

Gather feedback from the community.

User interface changes

The "top half" of the diff experience will undergo a facelift :-)

API changes

It's likely that this change will require a decorated diff controller.

Data model changes

None (hopefully)!