Browser cache & Uchiwa upgrade

[palourde]

Expected Behavior

When upgrading Uchiwa, all assets should be invalidated and the browser should be forced to download the assets again.

Current Behavior

A manual cache purge is still required sometimes.

Possible Solution

Cache headers and assets timestamp are already used. We need to figure out why the assets are not properly refreshed.

Steps to Reproduce (for bugs)

Context

See #665

Your Environment

• Uchiwa version used: 0.23.0
• Sensu version used: N/A
• Operating System and version (e.g. Ubuntu 14.04): N/A