Introduce a boostrap form builder.

This form builder add a .buttons form helper to simplify bootstrap
styled form submit buttons. It comes with a boot_form_for helper which
you can use as a drop in replacement for the stock form_for helper.
Port all forms to boot_form_for.
Merge branch 'features/ruby_212_rails_411' of github.com:panterch/future_kids into features/ruby_212_rails_411