Generate record stubs

First POC

Status:
* [x] Works for basic scenarios
* [x] Handle situation when LBrace is on a different line
* [x] Only generate missing fields
* [x] Do not display Smart Tag when all fields are filled out
* [x] Support ``let x = { Field1 = }`` expression
* [x] Support ``let x = { MyRecord.Field1 = }`` expression

See:
![record-stub-generation-1](https://cloud.githubusercontent.com/assets/1169339/2752096/7aed784a-c8fe-11e3-8e14-e225660cc416.gif)

![record-stub-generation-3](https://cloud.githubusercontent.com/assets/1169339/2772102/1a9ff8b2-ca77-11e3-9a90-94472510e702.gif)