[WIP] Added a floating banner to the diff view

Review Request #8740 — Created Feb. 11, 2017 and discarded — Latest diff uploaded


Review Board


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:

I tested the banner on the testing server. I have currently only tested the
banner for review requests containing one diff file.