Make TbFormButtonElement adhere to CFormButtonElement specifications:

- automatically set 'name' property (required for checking if form is submitted)
- use documented core types
- use custom widget if type does not match

http://www.yiiframework.com/doc/api/1.1/CFormButtonElement/
Merge pull request #253 from marcovtwout/bs3-improve-tbform-input-buttons

Make TbFormButtonElement adhere to CFormButtonElement specifications