Bust javascript cache on release

[jzohrab]

Currently, user browsers may cache public/js/lute.js, so when people update they don't necessarily get the latest code. Massively annoying for all.

The release process could easily do something like the following, as a very hacky but workable workaround:

• rename the file lute.js to lute_<somedatetime>.js
• change the reference to lute.js to match the screwy filename

This is all terribly hacky, of course, and the right thing to do would be something that I know nothing about, like WebPack. That belongs in a separate ticket; in the meantime, hacky hack above will do.

[jzohrab]

Using the current git commit short sha as a cache buster, lute.<short sha>.js.