add dense vector implementation
add a test checking dense vector interface
- rm _vector_type, operator[]
- rename getNRows() to size()
getNRows() was renamed to size()
changed to use inheritance here
define explicitly a copy assignment operator= which takes a scalar value for initializing all entries
- add operator<<  for Vector
- change an argument of Vector::write() from ostream to string (i.e. filename)
unsigned is replaced with std::size_t in Vector
replace spaces with tab for consistency
rename Vector class to DenseVector class
Removed the inheritance of DenseMatrix from MatrixBase.
Removed the inheritance relation of SparseMatrixBase to MatrixBase.
Removed the class MatrixBase.
Added a second template parameter for the index type.

Added a second template parameter for the index type to class template DenseMatrix.
DenseMatrix: added assignment operator, improved copy constructor.
Initial commit for class template GlobalDenseMatrix.
Added simple test for GlobalDenseMatrix.
Added move constructor and move assignment operator.
Changed return data type from int to bool for setValue() and addValue().
DenseMatix: splitted impl. and declaration.

Splitted declaration and implementation of class template DenseMatrix into
DenseMatrix.h and DenseMatrix.tpp.