RFE: Adjust Polar Efficiency for wind and night-time

[rgleason]

rgleason#97
There are some options which I (0zolli) often use on Sailgrib and I would like to see them implemented here:

Polar efficiency below 10kn TWS
Polar efficiency above 20kn TWS
Night time polar loss of efficiency

This is particularly useful with new or few crew onboard, or in case of conservative cruising.

Also new constraints added: (ideas that might fit well in the Configuration > Advanced Tab.)

1. When the boat speed is less than a given value, then motor at a given speed.
2. A point that would force routing to port or starboard

See rgleason#84

This is what Sailgrib does but a different way.
On Sailgrib you first make a route with any number of waypoints, then on each waypoint you can set to go to the waypoint or to let it on port or on starboard.

Then you let Sailgrib calculate the routing with this route and its constraints.

After the routing is calculated you can add a pivot point constraint anywhere on the isochrones and have it recalculated until you get what you want:

https://www.youtube.com/watch?v=4IkREAwjc-M

(Set English subtitles).