Previous State:

- The banner used to get added once per diff file. Thank you Simon Zhang 

for pointing out this bug. 

- The floating banner used to show even though the user was at the top 

of the page.

- The banner used to be bright green with a dark green border color.

- The banner contained the list of diff files only.

- The diff details inside the banner previously had its own styling class.

- The DiffReviewableView gets added to the DiffFileIndexView, which 

makes it tricky to keep track of each diff file for two different views. 

Since we are also adding a new diffFileIndexView to the FloatingBannerView

to display each diff file in the banner, we need to create a model that 

contains the state on what diffs are there or are loading.
Features Added:

- I changed the banner so that it only gets added once to the diff view, 

instead of once per diff file.

- I redesigned the styling so that the banner properly hides when the user 

is at the top.

- I added a white box that contains the diff file.

- I added some divs to the diff view that will be necessary in the future.

- I changed the banner color to match the review request body. The banner 

is now egg white with a black border color.

- I added a dropdown button on the right side of the banner (it currently 

lacks functionality).

- I removed this custom made styling class and reused the classes that have 

already been setup for this in diffviewer.less.

- I added a new DiffFileIndexModel class, but it is currently not connected 

to the views. This model class is still a work in progress.
Link to Demo Video:

https://drive.google.com/open?id=0B9Ti0bnAd2SuSmFvTWxudHFDdlU

I tested the banner on the testing server. I have currently only tested the 

banner for review requests containing one diff file.