crypt: Add time stamp to buffered messages

This is relevant when replaying the buffer on connect and brings the crypt module in sync with the normal logging functionality (which it bypasses).
crypt: Use ASCII for nick prefix and make it configurable

The previously hardcoded value of ‘\244’ is causing problems for clients which expect valid UTF-8 from the server/bouncer. This commit fixes #228.

The prefix is stored using a key of ‘[nick-prefix]’ in the general key/value store for the crypt module, which previously was only used for encryption keys.

This is not the best design, but the least intrusive one.