v0.4.4

• Allow removal of nullOption if a default value is set, fix #71
• Input className customization, fix #76
  1. added a className option to:
     • Textbox
     • Select
     • Checkbox
     • Radio
     • List
     • Struct
  2. handled in Bootstrap's skin:
     • Textbox: add the className to the <input type="text"/> / <textarea/> tag
     • Select: add the className to the <select/> tag
     • Checkbox: add the className to the <input type="checkbox"/> tag
     • Radio: add the className to all the <input type="radio"/> tags
     • List: add the className to the <fieldset/> tag
     • Struct: add the className to the <fieldset/> tag