[SPARK-4266] [Web-UI] Reduce stage page load time.

The commit changes the java script used to show/hide additional
metrics in order to reduce page load time. SPARK-4016 significantly
increased page load time for the stage page when stages had a lot
(thousands or tens of thousands) of tasks, due to the additional
Javascript to hide some metrics by default and stripe the tables.
This commit reduces page load time in two ways:

(1) Now, all of the metrics that are hidden by default are
hidden by setting "display: none;" using CSS for the page,
rather than hiding them using javascript after the page loads.
Without this change, for stages with thousands of tasks, there
was a few second delay after page load, where first the additional
metrics were shown, and then after a delay were hidden once the
relevant JS finished running.

(2) CSS is used to stripe all of the tables except for the summary
table. The summary table needs javascript to do the striping because
some rows are hidden, but the javascript striping is slower, which
again resulted in a delay when it was used for the task table (where
for a few seconds after page load, all of the rows in the task table
would be white, while the browser finished running the JS to stripe
the table).

cc pwendell

This change is intended to be backported to 1.2 to avoid a regression in
UI performance when users run large jobs.

Author: Kay Ousterhout <kayousterhout@gmail.com>

Closes #3328 from kayousterhout/SPARK-4266 and squashes the following commits:

f964091 [Kay Ousterhout] [SPARK-4266] [Web-UI] Reduce stage page load time.
[SPARK-4525] Mesos should decline unused offers

Functionally, this is just a small change on top of #3393 (by jongyoul). The issue being addressed is discussed in the comments there. I have not yet added a test for the bug there. I will add one shortly.

I've also done some minor renaming/clean-up of variables in this class and tests.

Author: Patrick Wendell <pwendell@gmail.com>
Author: Jongyoul Lee <jongyoul@gmail.com>

Closes #3436 from pwendell/mesos-issue and squashes the following commits:

58c35b5 [Patrick Wendell] Adding unit test for this situation
c4f0697 [Patrick Wendell] Additional clean-up and fixes on top of existing fix
f20f1b3 [Jongyoul Lee] [SPARK-4525] MesosSchedulerBackend.resourceOffers cannot decline unused offers from acceptedOffers - Added code for declining unused offers among acceptedOffers - Edited testCase for checking declining unused offers
Revert "[SPARK-4525] Mesos should decline unused offers"

This reverts commit b043c27424d05e3200e7ba99a1a65656b57fa2f0.

I accidentally committed this using my own authorship credential. However,
I should have given authoriship to the original author: Jongyoul Lee.
[SPARK-4525] Mesos should decline unused offers

Functionally, this is just a small change on top of #3393 (by jongyoul). The issue being addressed is discussed in the comments there. I have not yet added a test for the bug there. I will add one shortly.

I've also done some minor renaming/clean-up of variables in this class and tests.

Author: Patrick Wendell <pwendell@gmail.com>
Author: Jongyoul Lee <jongyoul@gmail.com>

Closes #3436 from pwendell/mesos-issue and squashes the following commits:

58c35b5 [Patrick Wendell] Adding unit test for this situation
c4f0697 [Patrick Wendell] Additional clean-up and fixes on top of existing fix
f20f1b3 [Jongyoul Lee] [SPARK-4525] MesosSchedulerBackend.resourceOffers cannot decline unused offers from acceptedOffers - Added code for declining unused offers among acceptedOffers - Edited testCase for checking declining unused offers