Free simple forms

For a new app, I'm using Bootstrap 3. The version of Simple Form that Alchemy needs does not offer generators for Bootstrap, so I loosened the dependency in Alchemy. That led to errors - which I fixed by substituting a lambda to a proc in the simple_forms initializer. That solutions comes from a change commit to simple_forms from April this year: https://github.com/plataformatec/simple_form/commit/c5cd96675ca413c5b9ea7f20bbe61a0410dbd59a.