add typescript sample project

[efredin]

I've restructured the /sample folder to include a javascript and typescript folder.

I did find a couple of issues with the initial typings definitions. If you choose not to keep the typescript sample as part of the project, we'll want to pull those out into a separate PR.

In order to test the typings locally from the sample project you'll need to link the intuit-oauth package with yarn or npm.

# Link local intuit-oauth branch with typings support to sample typescript project
yarn link
cd sample/typescript
yarn link intuit-oauth

[abisalehalliprasan]

@efredin This is good 👏 💯