Add a news page where release notes and custom news are displayed

Todo:

- [x] The headers sizes are completely out of control
- [x] Preprocess the notes so issues are linked correctly

![mahapps-news](https://f.cloud.github.com/assets/964691/2482616/9d822076-b0ef-11e3-80f5-d8a2952cb82e.PNG)

/cc @Amrykid I think you wanted this? :smile: