Added independent (non-wget) file downloads via open-uri.

Removed a bad vimeo_remote_test require from the remote test suite.
Added the UriUtilities class and a bunch of tests for it.
Included the ProgressBar class in the vendor directory so that the UriUtilities class can display a progress bar during downloads.
Added the ProgressBar tests to the test suite.
Added error handling to the main whatever-dl script for newly-possible IO/connection errors.
Removed the wget exec() call in favor of the open-uri call.