Added new baseclass: ILU0SolverBackend, for the combinations of a linear

solver and ILU0 (gets one argument less than other preconditioners).
Added some more backends and made RestartedGMRes work with this
structure. Therefore, the solve function of the baseclass is overloaded.


git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@6351 2fb0f335-1f38-0410-981e-8018bf24f1b0