Create Connection class

Also add g getter to models
Extract ModelCompiler class from Model.compile()
Extract __extends function
Some work toward support of indexes

- add IndexCreator class
- Mogwai and Connection inherits from EventEmitter
Update the way insert works
Rename field/fields to property/properties
Add Property class
Rename plugin and function definitions
Fix: Model.update() should now update all properties registered in the schema, instead of just "name" and "description" properties

This is a quick and dirty fix, though the method is still vulnerable to
Gremlin injection.
Merge branch 'develop'