Removed acceptance test.

In CI environment there is no running Redis instance. Trying to connect to resque-web makes no sense.
In CI environment, start Xvfb (virtual framebuffer to run acceptance tests in a visual environment) with a fixed resolution of 800x600.

This helps setting the correct environment for running acceptance tests which depend on the size of the browser viewport (e.g. Quick Reading mode tests, which need to know that when scrolling down some entries will be hidden above the viewport).

Inspired by the Travis CI docs here:

	http://about.travis-ci.org/docs/user/gui-and-headless-browsers/