User guestbook activator

Admin can de/activate user guestbooks in admincenter settings
![admin_settings_usergb](https://f.cloud.github.com/assets/4713304/1853989/270349c0-7715-11e3-8986-429e534cb755.png)

If Admin has activated user guestbooks for users, user can de/activate user guestbook in myprofile
![myprofile_active](https://f.cloud.github.com/assets/4713304/1854017/9b41ad04-7715-11e3-9b41-f63dd8fff058.png)

If Admin has activated user guestbooks for users and user has activated user guestbook, user guestbook will be displayed in user profile
![profile_active](https://f.cloud.github.com/assets/4713304/1854030/c8b892c0-7715-11e3-940e-39041eb0e181.png)

If Admin has deactivated user guestbooks for users, user can not de/activate user guestbook in myprofile and user guestbook will not be displayed in user profile
![myprofile_inactive](https://f.cloud.github.com/assets/4713304/1854081/a0a96cc2-7716-11e3-9058-42feeae90c27.png)
![profile_inactive](https://f.cloud.github.com/assets/4713304/1854057/546afcf4-7716-11e3-8b4f-22d2e0d1e2f4.png)

If Admin has activated user guestbooks for users and user has deactivated user guestbook, user guestbook will not be displayed in user profile
![profile_inactive](https://f.cloud.github.com/assets/4713304/1854057/546afcf4-7716-11e3-8b4f-22d2e0d1e2f4.png)