Make style and JS changes take effect immediately after deploying a version

Yesterday I deployed a CSS change and found that it took 1h after deployment for users to see it.  Also, the old 1h expiration meant that users were downloading these files again each hour.

The new way of serving these files puts the rietveld revision in the URL so that each different deployed app version makes a different request that will not use an old cached file.  Since we are no longer relying on expiration, we can let it default to 7 days and reduce the number of times users download it again.

[jrobbins (corp), 2014-08-12 17:27:59]

PTAL.

[rmistry, 2014-08-12 17:29:13]

LGTM

[jrobbins (corp), 2014-08-12 17:38:30]

This was committed as
https://code.google.com/p/rietveld/source/detail?r=dd40c8212dda15d9da93854838...