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)

If you think this should be in the client, please help testing.

Known issues, need to be solved before merging:
- New keypool addresses are not added to the dialog without a client restart
- Addresses don't change from (keypool) to (change) when sending a transaction without a client restart