Behat langimport tool fails randomly in Firefox

After pressing the "Install selected language pack(s)" button there is no output until the import has completed.

On latest Firefox, the algorithm to detect navigation determines that if there is no page change started after 200ms, that no page load is in progress and the call to elementClick ends. This is determined by the remote source starting to output.

We should add progress bar to the lang import tool and ensure that there is initial output, and that progress is reported the user.