Can now be used in the pure cmake as well as in the autotools/cmake
situation. In the end GRIDDIM and GRIDTYPE are define as cached variables.

This reverts commit 2e8a29f9f02fae28920147e17fc0406a57ca8524
and should work now since we're shipping the FindEigen3
script that's apparently missing from some current
cmake distributions

This reverts commit 043fbca5cadb4e4ef7909df0049aef350bb61d89.

refs #5

This reverts commit b5e571fc9ad2240d510514566c0946b2cce23426.

At the moment it is not trivial to configure a debug build with e.g. -O2.
Upon calling make cmake is called and the CMAKE_CXX_FLAGS_DEBUG are
appended to any given CMAKE_CXX_FLAGS, thus overriding any -O? given there.
Since the desired debug flag might vary from compiler to compiler
(-O0, -Og) anyway I propose to remove the -O? entirely from the debug
flags. Please revert or voice opinions!

* ensure dune-commons cmake stuff is used only with --use-cmake

* not sure if gcc and icc understand this

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