Extract type wrappers into a new package.
Use an embedded type for WrappedTime.

This is as close as we can get to a subclass in Go. It allows us to treat
the WrappedTime like a time, so we don't need to convert lots of `x.y` calls
into `x.Time.y` calls.

http://golang.org/doc/effective_go.html#embedding
Convert sig loading SQL to Cypher.
Use WrappedTime for signature values.
Dates in Neo have two formats.

I have no idea why this is happening, but the dates associated with keys
have one format and the dates associated with signatures and UIDs/UATs have
another format.

For now this somewhat ugly fix allows us to parse both.

Some dates go in one way, some go in the other way. So what?
User WrappedByteArray for signature Packet.