Chrome extension

Adds feature to browser that makes importing an issue quick and easy. Either click the icon in the browser bar or press `cmd+i` on OSX or `ctrl+i` on Windows.

![fantastical](https://cloud.githubusercontent.com/assets/623/3240693/3e764ed2-f130-11e3-9941-8b55550cddd5.jpg)


Closes #1 

- [x] Build Chrome extension
- [x] Deploy to Chrome store
- [ ] Build Safari extension
- [ ] Make available for distribution