Normalized task start/finish time in Web UI.

Review: https://reviews.apache.org/r/15539
Added terminated frameworks to frameworks tab.

In preparation for moving frameworks off the homepage, terminated
frameworks will now be listed on /frameworks.html.

The code was copy/pasted from home.html.

Review: http://reviews.apache.org/r/15526
Moved offers to their own tab and page.

In preparation for moving Tasks to the homepage, Offers moved to their
own page and tab. They are available as top-level navigation, and the
homepage table is now gone.

Review: http://reviews.apache.org/r/15527
Fixed an import error in futures.py.

When queue is empty, the name Queue.Empty must be imported.

From: Du Li <lidu008@gmail.com>
Review: https://reviews.apache.org/r/15585
Fixed the flaky pstree test.