Calendar today

Solves idea 489 (https://duck.co/ideas/idea/489/show-current-date) by implementing a replacement for wolfram-alpha calendar which also highlights the current date

See issue #332

![screenshot-calendartoday](https://f.cloud.github.com/assets/5677563/2190176/07beda90-9824-11e3-8458-53eb3cbf5d40.png)

PS: I hope I have done everything correctly, it's my first contribution...