[WIP] add folders for templates

[hiimbex]

This is only meant to be merged once create-probot-app has been update to take optional flags to select specific folders for probot app templates.

The main thing happening in this PR is:

• adding the contents of the repo into the folder basic-js
• adding the contents of probot/template-typescript into basic-ts
• adding the Checks API example from https://github.com/probot/probot/issues/620 into checks-js
• adding the Git Data example from https://github.com/probot/probot/issues/620 into git-data-js

Todo:

• [ ] fix tests on new examples
• [ ] test each example
• [ ] make necessary changes to create-probot-app