Added scaffolding for experimental/cartesian_test

- Build system updates
- Basic .cpp file.
Added class CartesianGrid.
Started on CartesianGrid. Segfaults in tests.

- Pushed to Github for backup.
CartesianGrid accessor methods now seems to work as expected for 2D.
CartesianGrid::cellAt now returns a reference.
Added stubs for CartesianGrid::faceAt.
CartesianGrid::faceAt seems to be working.
Fixed indexing bug in CartesianGrid::faceAt.
Updated tests to cover all cells and faces
Turn of D_GLIBCXX_DEBUG, even in EQUELLE_DEBUG-mode.

- Due to opmcore being built without it, even correct programs segfault.
Added CartesianGrid-ctor taking a parameterObject-

- Extracted out method CartesianGrid::init2D.
- Added unittest.
Added CartesianGrid::inputCellCollectionOfScalar

- Added CartesianGrid::param_ member.
Refactored tests and wrote heat equation test
Merge branch 'cartesian' of https://github.com/sintefmath/equelle.git
into cartesian

Conflicts:
	experimental/cartesian/src/cartesian_test.cpp
Added CartesianGrid::inputCellCollectionOfScalar
Merge branch 'cartesian' of https://github.com/sintefmath/equelle into cartesian
Added iPython notebook
Doxygen documentation fixes.
Merge branch 'cartesian' of https://github.com/sintefmath/equelle into cartesian
Try to speed up linking time of CartesianGrid