Add capability to provide confirmation phrase instead of password

Problem/Motivation

On the project I'd like to use this module for a majority of users have logged in via Google and thus do not have passwords the user knows.

Proposed resolution

Provide configuration to allow administrators to choose whether or not they would like to use a delete confirmation phrase rather than the user password

User interface changes

• Add configuration settings form
• Adjust logic in the CancelAccountForm to account for both user password input or a confirmation phrase

API changes

N/A

Data model changes

N/A