Added the ability to resend Account Verification Emails.

We're moving towards having the token concept be more of a 'behind the scenes' concept when possible.  So instead of a 'send token' feel, I'd like it to feel more like a 'send email' operation.  For example: 

```java
import static com.stormpath.sdk.application.Applications.*;
//...

application.sendVerificationEmail(verificationEmailBuilder().setLogin(login).setAccountStore(dir).build());
```
The request should have a builder so callers can inline conveniently.

Also note that the REST API is favoring `verificationEmail` and not `emailVerification`.  The former is a resource/noun which aligns with REST better than 'emailVerification' which is more of an abstract concept/process.

HTH!