switch to `download` module
add option passthrough to `download`
let `download` unzip for us
switch back to google storage for selenium release downloading
update fallback selenium version to 2.41.0
refactor parallel paths along selenium/chromedriver instead of versions/downloads
verify checksums of downloads
Merge pull request #6 from groupon-testium/etag-md5

verify checksum of downloads
Merge pull request #5 from groupon-testium/download-module

fix selenium.jar downloads