Instantiating a contract object in TypeScript results in a compiler error for view and change methods

[lantelyes]

When instantiating a contract in typescript, the viewMethods and changeMethods are not accessable in the resulting object, this is due to Object.defineProperty not being allowed to definitely assign properties via the constructor. See here for reference: microsoft/TypeScript#42919

To reproduce: instantiate any contract in TypeScript with a view or change method provided in the options parameter then try to call it, you will get the TypeScript error Property "methodName" does not exist on type 'Contract'.

I'm willing to take this on, the fix is fairly straight forward.