some revision on how to writing data to file

- CHG : move some of the method previously called in DDTest (Derived) to DDSolver (Base), in order to make the base class to be the major one.
- NEW : separate the previous file operator class to two part, a class to specially write and read file and a class to link the simulator and the former class
time evolution of dd solver is tested.

- FIX : fix a bug in building rhs vector in dd solver
- FIX : fix a bug in repeatedly solving dd problem