use parameters expressing weather conditions

[smaria]

The following parameters were determined to be variable depending on weather conditions:

• how far does the sheet go (/weather/SheetLength)
• laylines safety margin (/weather/LaylineMargin)
• waypoint position (this depends on how our waypoints are determined -> #52 )
• timeout for failed tack (/weather/TackTimeout)

[smaria]

108 makes the start on setting the sail wind specifically (though that ticket will not interpolate different wind conditions yet)