Allow optional object properties for typescript

[Pita]

This marks object properties as optional unless they are explicitly marked as required in the swagger file.

So this:

mytype: 
  required: 
    - foo
  properties:
    - foo
      - type: string
    - bar
      - type: string

now becomes this (notice the question mark)

type mytype = {
    'foo': string
    'bar' ? : string
};