Add retry logic to transfer creation

[maneatingape]

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• Issues list does not already contain this feature.

Is your feature request related to a problem? Please describe.

Celestial bodies sometimes get in the way of transfers, causing them to fail. e.g Mun when leaving Kerbin

Describe the solution you'd like

Return list of transfers in ascending order of cost, instead of just returning best transfer. If a transfer can't be made for some reason (e.g. an unwanted encounter with another body gets in the way) then try the next best transfer and so on.

Describe alternatives you've considered

The user could handle retry logic in their own scripts.

[ElWanderer]

I ran into this issue (in my case it was Jool blocking the optimal path to Eeloo) but there was no indication as to what had gone wrong, other than no nodes being created (until I turned off node clean-up). Is it meant to print anything to the terminal in this case?