Obstacles - Pathfinder

[mastrof]

Implements obstacles through Agents.Pathfinding.

Pros:

• All sorts of environments can be generated, all is needed is a walkmap which is nothing more than a BitArray
• Correctly integrates interactions with multiple close-by obstacles

Cons:

• There is only one possible type of "surface interaction" (i.e. the run is interrupted when it goes through an obstacle, equivalent to the old stick! function)
• Evaluation and storage of the walkmap with reasonable accuracy can be quite expensive (especially in 3D), but it's typically a one-time cost
• Integration of bacterial motion through an obstacle-dense environment shows widely fluctuating performance (in both time and memory)
• The resulting motion can be more or less strongly dependent on the resolution of the walkmap
• With current setup (defaulting to a trivial pathfinder), even obstacle-less simulations incur some extra performance penalty, scalability should be tested.

[mastrof]

Best strategy is probably to restore the old functionalities from f3edb4e. Both approaches would then be available and can be chosen depending on the particular problem details. However, the pathfinder stepping would need to be activated manually which makes things a bit messy.

[mastrof]

This also closes #10.