Follows up on previous binary file changes. This will allow the

frontend to render binary files for visual reviewing. This will

only display a diff if the binary file is a image. If the file is

a not a binary, exe for example, it will display this message 

'This is a binary file. The content cannot be displayed.' This also

fixes problems where if the same commit with a binary is upload

multiple times the backend would hard fail. Now it returns without

doing anything.

Walked through a standard review process: posted changes, 

interact with changes, commented, and posted changes. Also 

covered by previouse tests written for image review UI.