Alerts occupy the whole page width.
Added a support method in feature tests that waits for AJAX calls to be finished.

Inspired by this blog post:

  https://coderwall.com/p/aklybw

Hopefully this will help fix a failing acceptance test in Travis CI, in which the test is assuming that a "mark entry as unread" operation has successfully finished (because DOM changes have already happened) when in fact the AJAX call and therefore the change in the database is still running.