Add UI testing to share management

Added the necessary gems and configuration to support Capybara and
Poltergeist for the browser testing.

Also extracted the #start_daemon function from the sync test because it
is used in the share_management test, and will be used in other UI
tests.
Add integration tests to the repository browser

This now checks for of the features of the UI with 2 exceptions:
* viewing a non-text file
* uploading a new file

There a TODO both of these features, and I hope to re-visit them in the
future.