fix interpolation-bug when quaternions don't have the same sign. Thanks to Oliver Sander for the patch ;-)

[[Imported from SVN: r8102]]

[[Imported from SVN: r8101]]

[[Imported from SVN: r8058]]

[[Imported from SVN: r8034]]

[[Imported from SVN: r8020]]

[[Imported from SVN: r8010]]

[[Imported from SVN: r8009]]

[[Imported from SVN: r8005]]

[[Imported from SVN: r8004]]

[[Imported from SVN: r8003]]

[[Imported from SVN: r7984]]

add method to transform an embedded tangent vector into the corresponding SkewMatrix and use this method in the old tangentToSkew method

[[Imported from SVN: r7971]]

[[Imported from SVN: r7958]]

[[Imported from SVN: r7956]]

Add the cayley and inverse cayley mapping. By now these formulas use the matrix representation of a skew matrix/rotation which is not very pretty. I will replace it by a quaternion counterpart when I figured out how to do it properly 

[[Imported from SVN: r7943]]

[[Imported from SVN: r7933]]

[[Imported from SVN: r7932]]

[[Imported from SVN: r7931]]

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]]

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: r7568]]

[[Imported from SVN: r7563]]

move method getFirstDerivativesOfDirectors into the rotation class.  It does not make sense for general quaternions

[[Imported from SVN: r7562]]

[[Imported from SVN: r7374]]

[[Imported from SVN: r7352]]

[[Imported from SVN: r7351]]

[[Imported from SVN: r7341]]

[[Imported from SVN: r7314]]

fix sign bug in the series expansion of sin(x/2)/x.  Thanks to Jonathan Youett for pointing this out

[[Imported from SVN: r7095]]

[[Imported from SVN: r6816]]

[[Imported from SVN: r6808]]

[[Imported from SVN: r6807]]

[[Imported from SVN: r6756]]

[[Imported from SVN: r6754]]

[[Imported from SVN: r6752]]

[[Imported from SVN: r6741]]

I'll fix that soon.  I want to take the time and see how
much the behavior changes.

[[Imported from SVN: r6739]]

[[Imported from SVN: r6738]]

[[Imported from SVN: r6708]]