Add a PRO mode

[vicb]

The PRO mode would be available for sponsors or members and unlock more features.

The additional features are planned features - anything related to safety would not be PRO mode.

A few things I have in mind:

• Support for groups
• Change your live track color
• Change your icon (2D and 3D)
• "Real" live tracking
• Better track resolution
• Direct URL to a pilot/group location
• Stealth mode
• Save routes
• Save (live) tracks

Todo: intgerate stripe for subscription