Adding fix for sessions + verification.

There was a subtle bug when a user verified their account, what would happen
was:

- A user clicks the link in their email to verify their account.
- They are redirected back to the Stormpath application.
- Their token is verified and an account link is generated.
- We set the session data to the account HREF.

What we do with this change is:

- Lookup the account based on the returned HREF.
- Insert that into the session.

This fixes the flow behavior.
Adding changelog info.
Making postRegistrationHandler work for account verification as well.
Upating changelog.
Adding upgrading docs.
Version bump.