Look into cache busting uri based caching with require.js

[jakemac53]

The existing caching mechanism (etags with must-revalidate) causes a round trip per JS module.

For large projects this can cause many seconds worth of extra wait time even when talking to localhost, because chrome limits the number of concurrent requests (to 6 I think).

We could instead use cache busting uris to resolve this in a way that doesn't require round trips and allows us to set the cache headers to never expire.

Some considerations:

• how does whatever solution we come up with interact with hot restart?
• how can we know on the server side to set special headers for these files?