REST API V2

## Major Features:

- New, more RESTful API
- Builds on the V1 `scale` functionality, adding the ability to update arbitrary parameters (resource allocations, command, uris, constraints, container options, etc.) for an application, applied to subsequently launched tasks.
- Adds a new document to the repository providing a comprehensive overview of the available HTTP endpoints in both the V1 and V2 APIs, and an accompanying doc generation script.  This serves as an additional tool for integration testing.
- Adds a new `/help` endpoint with linked documentation detailing the usage of both the V1 and V2 APIs
- Adds more detail to all task JSON to indicate when tasks were staged and started.
- The Marathon web UI now uses the new V2 API.