feat(test/integration/utils.coffee): Utility function to download file

Since we cannot rely on Travis or other CI solutions to have files on their systems,
we resort to downloading a file remotely, saving it on the filesystem, and then
uploading it to the remote Selenium instance.
fix(Gruntfile.coffee): Look for *-test.coffee for integration tests

In order to decrease conflicts with other helpful libraries / files the Grunt task
which runs integration tests will automatically load all files ending with
"*-test.coffee".