Polyosam add features

Added options to
- start first sweep x meter from polygon border
- configure the entry circle radius
- configured the min turn radius

Now the last turn can be a half sweep back or half seep forward if the distance from last turn is less than full sweep distance.

All this modification is made to use this module with more confidence in professional photogrammetry.

This doesn't sound like a good idea... why should the distance in x (east) be considered, but not north?
e.g. when you fly a survey in north/south direction, this doesn't really make much sense...