Factor `showNotificationBar` out into ValidatingView.

When all settings require an explicit save, this functionality will be
shared between each view (with slight changes, e.g. click handlers.)
Change course settings to require explicit save.

Rather than asynchronously saving when a setting is updated, we now
prompt the user to confirm their changes and only persist the data if
they hit the save button. Lettuce tests are updated to expect this
behavior and some new ones are added.
Refactor and update acceptance tests around saving settings.
Make sure that changing grading cutoffs triggers a save confirmation, and reliable reverting of changes.
Remove outdated deleteKeys from advanced settings.
Update acceptance tests for course settings.
Fix validation in many cases, and ensure that the notification bar pops up correctly.
Fix many validation bugs and failing tests.
Merge pull request #301 from edx/peter-fogg/explicit-course-settings

Peter fogg/explicit course settings