Fix : Android password field now hides the user input in FormAuthenticatorActivity

In Android, when using fields configured with type `FormAuthenticatorFieldType.Password` in a `FormAuthenticatorActivity`, they display their values just like regular text fields. This pull request fixes the issue and gets password fields to hide their input values as expected.

Submitted under an [Apache 2.0 license](http://www.apache.org/licenses/LICENSE-2.0.html).