gtfstidy: Add support for swapping coordinates

[jbruechert]

Implement a check in gtfstidy that finds unrealistic goordinates (swapped longitude and latitude), and corrects them.

This could be done like the following:

• If the speed between two stops is MUCH larger then the overall average speed
• Note the second stop
• If the speed between the second and the next stop is unrealistic again, swap coordinates for the second stop