Split the gender code into its own module.

In the process, adding module support to KerbalStats :)
Rename GetNode to CopyNode.

This allows "GetNode" to be used for getting nodes within the kerbal node.
Add AddNode/GetNode/HasNode functions.

Now KerbalExt acts as a wrapper for ConfigNode.
Provide a means to get a KerbalExt from a ProtoCrewMember.
Start tracking experience.

I'm not sure I like the current implementation, but it's good for testing
things.
Include the license file: LGPL.