Merge pull request #96 from endJunction/MeshGenerators

Mesh generators
add ID to Mesh
Reorder members of Mesh.
correct path
add constructor taking sparsity in LisLinearSystem
add DenseLinearSystem (in progress)
add helper functions to release memory
add DiscreteLib in CMake
add TestDiscreteLib
save progress in DiscreteLib
need to include some other headers
add DiscreteLib in Doxyfile
link GeoLib to MathLib
change () to []
LisLinearSystem should be inherited from ISystemOfLinearEquations
complete DenseLinearSystem. testing it is not done yet
save progress in DiscreteLib
save
add sparsity object as a parameter for constructor in DenseLinearSystem
implement printout() in DenseLinearSystem