Move SJCL startCollectors call to ui.js

util.js is basically a bunch of polyfills now.
Pretend GeneralString is UTF-8

Stuffing UTF-8 in an ASN.1 GeneralString would make ITU-T sad, but
apparently this is what Microsoft does, although they also do
case-folding. MIT Kerberos just forwards the string it gets from the
caller, which is locale-specific. Given that, the most reasonable thing
for us to do is probably assume UTF-8.

Anything's better than the old UTF-16 vs byte string confusion. We
really need to move to using TypedArray.

Closes #41.