UUID implementation should use window.crypto

[tgr]

The UUID implementation uses Math.random() to generate random bytes. There are reports that on some browsers this function has poor entropy and UUIDs might conflict even with a relatively small log volume. On browsers which support window.crypto, that should be used instead.

[mattrobenolt]

Ah, neat. Should be easy to change up.

[mattrobenolt]

Fixed with #349