qt: add "Show all" option in "receiving addresses"

Extra information for nosy people.
Add "Show all" option in "receiving addresses" to show change, keypool, refund etc addresses. These can only be viewed, not edited.

![showall_disabled](https://f.cloud.github.com/assets/126646/1723290/95f6fe5a-6255-11e3-9ed9-2365bc091f31.png)
![showall_enabled](https://f.cloud.github.com/assets/126646/1723291/960b9c2a-6255-11e3-8836-029b0a2a11ac.png)