Investigate: swap pointer instead of copying fields #165
Description
After using a solver like Advection Solver it is necessary to copy the solution into the temporary fields. The function call advect(Field out, Field in, [...]) consists of the ourput field where the calculated solution is stored and the input field where the current solution is stored. to pass the solution to the next solver the current solution has to be as well in the temporary field, which will be the next in Field.