Couple of changes to the selenium tests

Quit early if unisubs-integration is not present.

Added a couple status code checks
Speed up wait_for_* functions
Added submit_by_css()

This works faster than click_by_css(), because selenium doesn't have
to move the mouse.
Faster login for selenium tests

Instead of navigating through the login page, we just set the
session/cookie data directly.
Don't save screenshots after each unittest

Saving a screenshot takes about 5 seconds per screenshot.  Janet has a
way better way to capture info about failures using saucelabs.
Allow selenium tests to re-use the browser

If the test class sets NEW_BROWSER_PER_TEST_CASE = False, then we will
only create a new browser once per class.  This results in a huge
speedup if there are many test methods.
Merge branch 'dev' of github.com:pculture/unisubs into selenium_perf
Merge branch 'dev' of github.com:pculture/unisubs into selenium_perf
Merge branch 'dev' of github.com:pculture/unisubs into selenium_perf
initial rounds of performance changes from ben with a few tweask
updates to the rest of the tests to use speed updates
missed these tests
Merge pull request #71 from jdragojevic/selenium_perf

selenium performance: Ben's changes to make test run fast and updates to the tests to use them.