Implement PasswordStepPane

**Description:** implement `PasswordStepPane`. To do so, improve the wizard code to allow steps to disable the next button as a pre-requirement.
**Testing:** manual for the GUI part and added a UT for the password validation.
![image](https://cloud.githubusercontent.com/assets/259587/3257869/8389873e-f232-11e3-81c9-37e0a9887b44.png)