Node/Connection deserialization

Deserialization for nodes and connections! I only did some basic testing
but everything seems to be good.

Attributes are pretty FUBAR and we definitely need to refactor how they
work in the future, but as far as I know they're not necessary for our
MVP.

Constraints are also still pending.
Basic attribute bindings

Quickly threw this together, of course it could be much better...

I think we want some kind of method like TypeValue#createInstance(...)?
Would make this a lot easier
checkstyle pls...
adding boolean check
Merge pull request #138 from maxqchen/master

Node/Connection deserialization :shipit: