Merge pull request #17 from endJunction/merge-DiscreteLib1

Merge discrete lib1
Extract part of TestLinearSystem test to 2Ddiffusion.

This removes gtest and LIS dependencies and simplifies code coverage.
Add coverage make target for 2Ddiffusion.
Remove ghost point functions. All unused.
Remove other unused functions from DofEquationTable.
Remove DoF/SequentialEquationStorage.
Remove IEquationStorage::size and hasEquationID.
Remove RandomEquationIdStorage::pointID.
Limit DofEquationIdTable::construct to random, by points.

Only (!DofNumberingType::BY_VARIABLE) and random equationID storage is used.
This removes setAll and activate from IEquationIdStorage too.
In DofEquationIdTable::mapEqsId local numbering type is BY_VARIABLE.

Remove other case.
Remove one of unused DofEquationIdTable::addVariableDoFs.
Remove IEquationIdStorage::activate.
Remove unused RandomEquationIdStorage's ctor.
In RandomEquationIdStorage inline print_map in printout.
Remove all ElementWiseVector{LocalAssembler,Updater}.
Remove unused IDiscreteSystem add/delete LinearSystem/Vector calls.
Remove unused DiscreteResourceManager.
Remove all of DiscreteVector related code.
Remove unused IDiscreteLinearSystem::setZero and addRHSVec.
Remove unused DiscreteObjectWithID.