Limit foraging trip distance

@mlange @nolzen As discussed this models the limited foraging distance of the central foragers as a kind of attractive force that kicks in at half the maximum range and at and beyond that range completely determines the movement direction during exploration, i.e. will turn the insect straight back towards its nest/colony.

With the current values taken from literature examples, this does not have a large effect, but it can be clearly seen when ridiculuously small values are used, e.g. 5m for solitary bees and 15m for bumbleb bees yields: