The red, green, and yellow colors used in Review Board's diff viewer aren't

easily dintinguishable for users with various colorblind disabilities. 
To address this, icons have been added to inserted, replaced, and deleted

diff viewer lines (+, ~, and - respectively) to visually represent the type

of change made without having to solely rely on color. Alignment for equal

lines (unmodified lines of code) was also updated; line numbers for all

diff types should now be aligned.
I've attached a video below showing how the diff viewer would like with my

new changes.
For more information on how I came up with these changes, see my notes here.

All current unit tests pass. No additional tests were made.