TEST: Add IE testing

[varjmes]

Some of the tests pass before we get delays (just like last time). I think there must be something happening in some of our tests that just aren't working with IE10/11.

https://github.com/defunctzombie/zuul/issues/121#issuecomment-119670847

I don't think IE10/11 saucelabs is broken themselves, as others seem to have it work for them: https://travis-ci.org/visionmedia/superagent/jobs/75516113\

I think we need to start with whatever tests comes after:

<internet explorer 11 on Windows 10> console
# adds object to db

I'm going to open a new PR and add some other browsers to test in.

[nolanlawson]

FYI, when I run the PouchDB test suite in Microsoft's VMs, IE10-IE11 all work swimmingly in all versions of Windows. However on Sauce it's another story; only Windows 8 and IE 10 actually work consistently. (Yes, even 8.1 has issues.)

If you want to be 100% certain, I recommend checking our Travis config which shows exactly which versions of Sauce's browsers we are using.

Another browser that mysteriously does not work at all in Sauce is Android <=4.4. Only 5.0 works. (When I test 4.0-4.4 locally in emulators/real phones, everything works fine.)

[gr2m]

Thanks Nolan!