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]]

It seems dangerous: I tend to get confused what these arguments
are.  Plus, the method is unused.

[[Imported from SVN: r7890]]

[[Imported from SVN: r7889]]

[[Imported from SVN: r7888]]

[[Imported from SVN: r7887]]

[[Imported from SVN: r7886]]

simplify the code by making the AverageDistanceAssembler accept the interpolation weights in a std::vector of FieldVectors

[[Imported from SVN: r7885]]

[[Imported from SVN: r7884]]

It's result is not necessarily a Rotation, hence such a method
would better be placed in the general 'Quaternion' class.

Also, nobody in this module used it anyways.

[[Imported from SVN: r7883]]

[[Imported from SVN: r7882]]

[[Imported from SVN: r7881]]

[[Imported from SVN: r7880]]

[[Imported from SVN: r7879]]

[[Imported from SVN: r7868]]

[[Imported from SVN: r7867]]

[[Imported from SVN: r7866]]

[[Imported from SVN: r7865]]

framework wants a global function space basis.

So far the P1 basis is hardwired for simplicity.

[[Imported from SVN: r7863]]

[[Imported from SVN: r7860]]

[[Imported from SVN: r7856]]

[[Imported from SVN: r7848]]

[[Imported from SVN: r7847]]

[[Imported from SVN: r7843]]

[[Imported from SVN: r7842]]

[[Imported from SVN: r7841]]

[[Imported from SVN: r7840]]

Computation of analytical energy gradients doesn't work, yet.

[[Imported from SVN: r7839]]

[[Imported from SVN: r7838]]

[[Imported from SVN: r7837]]

We need the extra flexibility for higher-order functions.
Run-time loss is around 1% -- that's okay.

[[Imported from SVN: r7836]]

[[Imported from SVN: r7620]]

[[Imported from SVN: r7617]]

[[Imported from SVN: r7616]]

[[Imported from SVN: r7614]]

[[Imported from SVN: r7613]]

[[Imported from SVN: r7611]]

[[Imported from SVN: r7576]]

notably the almost-equivalent UnitVector<4>: A vector with three entries
is interpreted by the UnitVector<4> class as a tangent vector given in
the basis returned by orthonormalFrame.  That is correct as it works
for all kinds of manifolds.  On the other hand, the Rotation<3> class
interprets as a 3x3 skew matrix (a tangent vector at the identity in
the matrix representation) even though the implementation used quaternion
coordinates.

To trick around this the use of exp methods with FieldVector<3> is avoided
by this patch.  A real fix would involve introducing a SkewMatrix class
and using that in Rotation<3>.

[[Imported from SVN: r7575]]

[[Imported from SVN: r7574]]

[[Imported from SVN: r7573]]