And use it in the test.

This patch uses the new 'constexpr' macro.  Hence it is C++11 only.

[[Imported from SVN: r9195]]

It makes it difficult to be sure that an explicitly
requested type is really handed over to every place.

While we are at it: reverse the order of the template
parameters.  Now first comes the type, then the dimension.
This is more like FieldVector and friends, and hence
should be less confusing.

[[Imported from SVN: r8148]]

[[Imported from SVN: r8146]]

needed to make the targetspacetest.cc test case pass.

[[Imported from SVN: r8041]]

[[Imported from SVN: r8040]]

[[Imported from SVN: r8039]]

[[Imported from SVN: r7991]]

And use it to implement the Rotation<3> class.  This makes the
Rotation implementation easier to understand.  Previously we
have used a FieldVector<3> when a skew matrix was meant.
This leads to confusion now that we also use quaternions as
tangent vectors of SO(3).  In local coordinates, these also
have 3 entries.  Adding the new skew matrix class makes it
clearer what kind of mathematical object is meant.

[[Imported from SVN: r7897]]

[[Imported from SVN: r7611]]

[[Imported from SVN: r7573]]

[[Imported from SVN: r7427]]

[[Imported from SVN: r7415]]

[[Imported from SVN: r7374]]

[[Imported from SVN: r7342]]

[[Imported from SVN: r6750]]

[[Imported from SVN: r6748]]

[[Imported from SVN: r6708]]

[[Imported from SVN: r6707]]

[[Imported from SVN: r6705]]

[[Imported from SVN: r6704]]

[[Imported from SVN: r6389]]

[[Imported from SVN: r5931]]

[[Imported from SVN: r4052]]

[[Imported from SVN: r4049]]

[[Imported from SVN: r4045]]

[[Imported from SVN: r4017]]

The class 'Configuration' is now called 'RigidBodyMotion', and can be parametrized by the space dimension

[[Imported from SVN: r4003]]

renaming the file 'configuration.hh' to 'rigidbodymotion.hh', which is a lot more meaningful.  Renaming the actual class will follow in a second.

[[Imported from SVN: r4002]]

[[Imported from SVN: r3488]]

[[Imported from SVN: r905]]

[[Imported from SVN: r737]]