Improve application introduction messages

Created by: SunilMohanAdapa

No every application that we have currently introduces itself properly. Update all application messages to provide the following consistently.

• Explain in simple non-technical terms what the application is about with links to more information from the project site.
• Provide any FreedomBox specific information about the application
• Provide clear instructions on how to use the service including links to desktop/mobile applications.
• Provide a launch button if the application provides a web interface.

Specifically this also includes:

• Improve the 'Apps' screen message.
• Explain how Tor works.
• Reorganize Tor page (see #1972).
• Explain a bit more on how PageKite works and how to create an account.