Adding new PlatypusTS todo app.

PlatypusTS is a framework focused on assisting with writing scalable cross-platform applications. The framework is written in TypeScript in order to take advantage of features such as static typing, enhanced tooling, and future ES compatibility. It is possible to write a vanilla JS app using PlatypusTS, but the recommended approach is to embrace TypeScript.

Included are unit tests in the tests directory. There is also a tests.md which shows the output of the mocha, grunt, and karma tests.