Distinguish club applications (external vs. internal)

[esinx]

We currently provide the option of either using:

• Penn Clubs as application submission management system, allowing the user to send acceptance / reject emails through Penn Clubs as well as customizing many more aspects of the application
• Some external provider (Google Form, Airtable, etc.) by providing a link to the application

The application creation form still asks for templates for external providers, we should eliminate the use of templates.