Use sjcl.random.startCollectors

This starts entropy collectors before getting any random values from SJCL.

I couldn't figure out how to actually test that the listeners for collectors had actually been added (these https://github.com/bitwiseshiftleft/sjcl/blob/master/core/random.js#L243..L254) so I left the test blank. If anybody can figure it out, that would be great. I decided to add the test because, looking for documentation or reference, I noticed that SJCL's random class isn't tested itself <sup>yeah...................................</sup>

If an application desires to start entropy collection before calling `authorize` or `generateAccount` they can call `crypton.startCollectors()` when the page loads.

Closes #69 on merge.