* Add a wider diversity of `gui` options
Although I know we want to remain less tied to the GraphQL Playground
GUI options, we definitely want to support a wider variety of options to
be passed in. This adds support for specifying partial options either
statically or dynamically for the gui, which can be extended to allow
for a wider array of guis than only GraphQL playground.
* Add boolean option and configuration for tabs
* move gui setting into ApolloServer Constructor
* document playground configuration in the constructor
* update playground types and fixed micro + koa integrations
* change gui to playground
* docs: change gui to playground
* fix logic for playground creation
* koa integration
* use koa-bodyparser v3 for node 6 support
* use middlewareFromPath instead of koa-router
* use async/await in koa fileUploadMiddleware
