Bootstrap 3 support

- [x] Install bootstrap 3 using bower
- [x] Review the header
- [x] Review the breadcrumb
- [x] Review the horizontal form
- [x] Review the comments form
- [x] Create a vertical form
- [x] Review the footer
- [x] Remove the vertical/horizontal toggle
- [x] Use Simple Form 3 generated initializers
- [x] Extract the wrappers configuration to Simple From
- [x] Add errors to example page

Closes #24 #26 

Related

https://github.com/twbs/bootstrap/issues/9067