432: Cancel Email Address Change

Issue: https://github.com/NuGet/NuGetGallery/issues/432

If there is an unconfirmed email address the user can now always reset it to the current confirmed email address.

Some screenshots:
Nothing changed so far:
![image](https://cloud.githubusercontent.com/assets/756703/3364657/5dfa5d1a-fb22-11e3-8d6a-72c564f5b1db.png)

With an unconfirmed email address:
![image](https://cloud.githubusercontent.com/assets/756703/3364673/8ad8a382-fb22-11e3-9eab-eefd38fc65ec.png)

The "Reset.." behaves the same as "Reset" API Key - after the postback:
![image](https://cloud.githubusercontent.com/assets/756703/3364702/ef9a6ca6-fb22-11e3-9f0a-4749715250bb.png)


The "Reset..." button is only visible when the current user has a confirmed email address.
![image](https://cloud.githubusercontent.com/assets/756703/3364740/6d25c4ea-fb23-11e3-95b0-551d4263d467.png)

Added also some tests for the auditing and the userservice.