Dev

- [x] Change help-tab to inline rather than iframe in to meet WordPress.org submission requirements
- [x] Add support for images (http://getbootstrap.com/css/#images)
- [x] Add support for progress bars (http://getbootstrap.com/components/#progress)
- [x] Add support for page header (http://getbootstrap.com/components/#page-header
- [x] Improve list groups, add support for linked items and custom content (http://getbootstrap.com/components/#list-group)
- [x] Add support for button dropdowns (http://getbootstrap.com/components/#btn-dropdowns)
- [x] Add support for breadcrumbs (http://getbootstrap.com/components/#breadcrumbs)
- [x] Add support for button-toolbar in button groups (http://getbootstrap.com/components/#btn-groups-toolbar)
- [x] Add support for navs (http://getbootstrap.com/components/#nav)
- [x] Remove "strong" parameter from alerts --this should be handled in the wrapped content
- [x] Allow arbitrary classes in columns