topleft/topright options, compact style, LESS, namespaced events

Add topleft/topright options (opens: 'topleft' or 'topright') for
positioning
- As a result, position is updated when months change

Add new 'compact' style for tighter display (option compact:true)
Add .less file to generate datepicker.css using bootstrap
variables/mixins for seamless integration
- Included mixins.less and variables.less from bootstrap 2.2.2

Looks like I also namespaced the datepicker events. No functionality change, but it lets a developer remove a datepicker. Eg:
```javascript
// Create date range pickers
var pickers = $('input.datepicker').daterangepicker();

// Remove date range pickers
pickers.each(function(){ $(this).data('daterangepicker').container.remove(); }); // Remove markup from document
pickers.off('.daterangepicker'); // Remove namespaced events (click, focus, etc.)
pickers.data('daterangepicker',null); // Remove daterangepicker data object
```