Add default_form_class and allow form class overrides

This is especially useful with bootstrap forms where you might want to
switch to a `form-inline` layout even though the default is a
`form-horizontal`.

This deprecates SimpleForm.form_class in favor of
SimpleForm.default_form_class.

e.g.
config.default_form_class = "form-horizontal"
simple_form_for @user, html: { class: "form-inline" }
Updated changelog for default_form_class
Test with Rails 4.2
Remove all warnings of invalid CSS selector
Add label to NO_STIP list of rails-dom-assertion

Related with rails/rails-dom-testing#15
Fix invalid selectors
Who cares about rubinius?
Use latest versions
Call full_messages_for on model errors instead of on model itself
Added test for full_errors_on_association bugfix
Use the right wrappers as default

As can also be seen in https://github.com/rafaelfranca/simple_form-bootstrap/blob/master/app/views/examples/_basic_example_sf.html.erb#L2 these are the wanted wrappers.
Merge pull request #1136 from mvdamme/full_messages_for_bug

Fix full_messages_for bug for associations
Update changelog [ci skip]
Fix wrapper options support for boolean types
doc how to get html 5 date / time inputs
:date not :datetime in the html 5 example
Merge pull request #1150 from nruth/patch-1

doc how to get html 5 date / time inputs
Improve html 5 notice [ci skip]
Test with master
Assert the absent of tags not the escaped text

Nokogiri doesn't escape the output