Draft: Reduce vertical height of version control header, file headers, and diff expansion rows

What does this MR do?

• Changes version header buttons/dropdowns to small size
• Reduces height of version header
• Reduces height of file headers
• Reduces height of diff expansion rows
• Removes file changed icons

Why?

To de-clutter the page slightly, and provide a little more room for the actual diff files.

Screenshots or Screencasts (strongly suggested)

Before	After