Fix flaky tests

And remove .travis.yml file.

Copied from https://github.com/django/django/pull/3121/files#diff-f6d1c75ec606389da5af6558bf57f171

See code comment for more info. Unfortunately, I wasn't able
to find anything better than time.sleep().

We would often see 'Broken pipe' errors pulluting the logs when running tests.
Broken pipe errors occur when browser aborts connection. It can be because
the browser was navigated to a different url before the current page finished
loading, but it could also be because it started downloading an image, but decided
that the image didn't change after loading part of it, and aborts the connection
to use the version from the cache.

The broken pipe errors are benign and are actually suppressed by default in Django 1.8.

The scrolling is not entirely precise, it's sometimes off by a pixel or two.
Increase the tolerance to 2 pixels.

Competing Evidence: Fix issues from client QA

The videos have to be resized after each step is displayed,
because they are sized to fit into their container at load time,
but since the container isn't visible at load time, the videos
end up with wrong dimensions.

Trigger video resize after displaying each step.

The scrollIntoView function can be called multiple times,
which resulted in multiple (10+) scroll animations getting queued.

After the first animation successfully scrolled to the top of the step,
the others kept running one by one. The animations weren't visible
because the element was already scrolled to its final position, but if
you tried manually scrolling down while the animations were still running,
the window would be scrolled right back up.

A small light grey copyright notice is displayed below the buttons
of mentoring and step blocks.

It is hidden in the apros theme.

Also includes a drive-by fix that makes integration tests for plot
blocks more robust.

Fix a few layout issues in Step Builder

Refactored Step Builder Messages

* Change conditional message configuration to strings (better XML)
* Don't use student_view for embedded content in Studio or XBlock workbench

Step Builder: Fix JS error that causes crash if no review step is present

Step Builder: Make sure tooltips for plot points work across different browsers

Fix various bugs found in QA