Add exceptions for DropPoint, Location, Capacity
Add exceptions for DropPoint, Location, Capacity

* The constructors now raise exceptions if something is wrong with the parameters
  or the object could not be created as wanted.
* Maximum length of location descriptions and default crate count of capacities
  are now static class variables.

der-michik/c3bottles,der-michik/c3bottles,der-michik/c3bottles,der-michik/c3bottles