Remove all extraneous spaces in plugin.yml
Rewrite payment code

The main class is now called PaymentManager, and it automatically picks the first PaymentHandler that is enabled and available.
The dt.nocost permissions were redone to make it easier for the PaymentHandlers.
A message was added for when the trip is free (does not apply under FreePaymentHandler).

Some assorted changes were thrown in by accident - the != -> == in FlightsDB was a clear bug.
Add sk89q's command framework as shaded library
Whoops - forgot to add Flight as ConfigurationSerializable
WIP 1 in reimplementing with WE command framework
startFlight() and hasFlightPermission() now take a CommandSender
WIP 2 of sk89q command framework, redo permissions