Add support for input group #60
Add support for input group #60

Issues #60

Usage
```php
{!! BootForm::text('tel', 'Phone', null, ['suffix' => BootForm::addon('button', 'Call', ['class' => 'btn-success'])] ) !!}
{!! BootForm::text('tel', 'Phone', null, ['prefix' => BootForm::addon('button', 'Call', ['class' => 'btn-success'])] ) !!}
{!! BootForm::text('tel', 'Phone', null, ['prefix' => BootForm::addon('icon', 'dollar')] ) !!}
{!! BootForm::text('tel', 'Phone', null, ['prefix' => BootForm::addon('text', '1-'), 'suffix' => BootForm::addon('icon', 'phone')] ) !!}
{!! BootForm::text('tel', 'Phone', null, ['prefix' => BootForm::addon('button', 'Call', ['class' => 'btn-success'])] ) !!}
{!! BootForm::text('tel', 'Phone', null, ['suffix' => BootForm::addon('button', 'Boom!', ['class' => 'btn-danger']), 'prefix' => BootForm::addon('button', 'Call', ['class' => 'btn-success'])] ) !!}
```
dwightwatson/bootstrap-form