some modification for Dirichlet boundary condition test

- NEW : add the method for testing Dirichlet boundary condition
- NEW : add the method for refreshing coefficient matrix due to the refresh of boundary condition in testing Dirichlet boundary condition
- NEW : add the method for refreshing a row of Dirichlet BC in the matrix class
- ENH : add virtual method of refreshBnd in DD solver, which is inherited in the DDTest class. The latter can call the methods for refreshing boundary current and refreshing boundary electron density for testing.
- ENH : show simulation time step
Merge branch 'DirichletTest' into NeumannTest
the version for Neumann boundary condition testing
Merge branch 'NeumannTest'