Add button 'Restore default roles and permissions'.

#4636


We now have the full process, see screenshots below (added steps 3 & 4):


Step 1: At first, the VSite uses the default roles and permissions so the checkboxes are disabled.
![toggle-1](https://f.cloud.github.com/assets/3273122/1700493/d1d1ff2e-601b-11e3-8239-c88402c34589.png)

Step 2: Clicking on the "Edit" button leads to confirmation page.
![toggle-2](https://f.cloud.github.com/assets/3273122/1700494/d41c1346-601b-11e3-9cd9-7c63535e2199.png)

Step 3: After confirmation, the VSite now uses its custom roles and permissions so the checkboxes are enabled.
![toggle-3](https://f.cloud.github.com/assets/3273122/1700495/d5de5ce8-601b-11e3-9a1e-7bb3582aeb5c.png)

Step 4: Clicking on the "Restore default" button leads to confirmation page. After confirming, we'll be back on step 1 again.
![toggle-4](https://f.cloud.github.com/assets/3273122/1700496/d723a4e6-601b-11e3-94c5-8c726ccd6270.png)