Configure reCAPTCHA for password reset

For password recovery, to optionally enable reCAPTCHA V2 in the Abiquo UI, add reCAPTCHA keys to Abiquo.

Go to the recaptcha site and request keys for V2: https://www.google.com/recaptcha/admin#createsite
On the Abiquo UI server, edit the client-config-custom.json file and set the public key
```
"client.captcha.publickey" : ""
```
On the Abiquo API Server, edit the abiquo.properties file and set the private key
```
abiquo.captcha.private.key=
```

If one key is present and the other key is missing, the platform will display an error message, and the user will not be able to recover their password.