- move STTR macro to StringUtil

- remove template from BoundingBox

- refactoring

-> LOW: low important message

- finding the sparse indices as an extra step in MultipleGridBuilder

- bugfix simulationfilewriter

- extract field from grid
- still not working

- sphere example: the inital values look good, but it started to crash from the interface after 1 timestep

- find stopper overlap grid nodes
- erase other nodes

- implement this methods in cuboid: next sphere + setnodes out of the object to invalid

- refactoring