Update the bootstrap generator to work with Bootstrap 3

See https://github.com/rafaelfranca/simple_form-bootstrap/pull/28
Remove note about working only with bootstrap 2.3
Update the tests
Fix error classes
Put a whitespace before the inline_label if it is present
Update CHANGELOG [ci skip]
Merge pull request #1008 from plataformatec/rm-space-on-inline-label

Put a whitespace before the inline_label if it is present
Add CHANGELOG entry [ci skip]
Merge pull request #1004 from plataformatec/rm-bootstrap-3-generator

Update the bootstrap generator to work with Bootstrap 3
Only call order when the given association responds to it.

Fixes #966.

This check is necessary because the given association may not respond to `order`.
Add CHANGELOG entry.
Check if the relation responds to `order`, instead of checking the
`reflection`.