This adds support for printing all buttons in a single row, as bootstrap expects them to be (as mentioned in #114).

The syntax used on the form objects is:

  ->add('buttons', 'form_actions', [
      'buttons' => [
          'save' => ['type' => 'submit', 'options' => ['label' => 'button.save']],
          'cancel' => ['type' => 'button', 'options' => ['label' => 'button.cancel']],
      ]
  ]);

Caveat:
Bootstrap relies on the presence of whitespace between buttons to show them with proper spacing. Since most of the form stuff in symfony is encapsulated by spaceless at one point or another, the only way to ensure space between buttons is by using a  . Which i did in the template.
Another possible solution is to add a custom style that adds the margin, but this breaks the "don't touch bootstrap" way of things and adds custom CSS, probably not a good idea.
I'll let @florianeckerstorfer weigh in on this.

To Do:

• Add Custom Type for Button Groups
• Add proper rendering blocks and handle proper off-setting
• Add constraint to only allow buttons in the group
• Tests?
• Brush off code with phpdocs and etc.