Add vec mat interface

* Note this this branch has been created based on other pull request #133.

This request includes the following changes under MathLib/LinAlg
- introduce Vector object: interface `VectorBase`, dense vector `Vector`
- improve the Matrix object interface `MatrixBase`
- delete SystemOfLinearEquations classes and instead use Solver classes which takes a matrix and vectors as input, e.g. `Solvers/DenseDirectLinearSolver.h`
- add Lis version implemenation in MathLib/LinAlg/Lis
- add a new test case for LinAlg, Tests/MathLib/TestLinAlg.cpp