Add support for class/object type/field checking.

[trezm]

This should take one of the two forms;

1. A class declaration should create a TDClassDeclaration object that has references to its types and methods. When there are static object calls, we can then check
   a. if the method exists
   b. if the method has the correct params/return type
2. A header file that contains the same metadata as a normal class declaration but can exist outside of an existing JS file. This is useful for defining typings for external files.