Refactor of E2E tests

This is a major refactor of the E2E tests.  We've moved most of the tests that were here to edx-platform and made substantial changes to bok-choy.  This refactor brings the E2E repo up-to-date with those changes.

1) Page objects are installed from edx-platform.
2) Simplified Vagrantfile and README
3) Removed marketing tests
4) Rewrote LMS and Studio tests to use bok-choy v0.1.0.  Removed some tests that are too low-level for the E2E suite and were duplicated in edx-platform.
5) Configured screenshot on failure

@jzoldak