A bootstrap-like theme

I have added a bootstrap-like theme.
It's not totally like bootstrap but it's easily customizable, I've done the CSS with SASS so you can quickly change the color and the style of the selected buttons. See ".selected-button" class and _mixins_and_vars.scss file

There are also minor changes in Picker.Date.js : 
- Changed the type of the Datepicker time ok input to button 
- And moved the separator div in between the two inputs (in order not to be forced to position them in absolute)

Here are some captures, hope you'll like it!

![Screen Shot 2012-12-13 at 10 57 57 PM](https://f.cloud.github.com/assets/445045/11986/34ce3678-4570-11e2-9197-0427bcd7bee9.png)

![Screen Shot 2012-12-13 at 10 58 04 PM](https://f.cloud.github.com/assets/445045/11987/3919041a-4570-11e2-9171-5cd893d3560c.png)