make sure the fd hessian is symmetric; hardwire Dexp(0) for more speed; use symmetry when computing the differential of the geodesic interpolation

[[Imported from SVN: r2016]]

[[Imported from SVN: r1792]]

[[Imported from SVN: r1769]]

[[Imported from SVN: r1719]]

[[Imported from SVN: r1718]]

[[Imported from SVN: r1716]]

[[Imported from SVN: r1715]]

moved the quadrature orders for bending and shear stuff into the header, as a first step towards reduced integration

[[Imported from SVN: r1714]]

[[Imported from SVN: r1713]]

[[Imported from SVN: r1712]]

[[Imported from SVN: r1709]]

[[Imported from SVN: r1703]]

[[Imported from SVN: r1701]]

[[Imported from SVN: r1700]]

[[Imported from SVN: r1698]]

[[Imported from SVN: r1677]]

[[Imported from SVN: r1658]]

[[Imported from SVN: r1652]]

[[Imported from SVN: r1632]]

bugfix in getResultantForce: get index of correct cross-section orientation from the index set instead of having 0 hardwired here

[[Imported from SVN: r1594]]

[[Imported from SVN: r1529]]

[[Imported from SVN: r1524]]

[[Imported from SVN: r1506]]

Add a method to assemble the Hessian matrix by a finite difference
approximation.

[[Imported from SVN: r1504]]

fixed one indexing bug in the hessian computation; added various helper methods for the derivatives of the strains and fd approximations for them

[[Imported from SVN: r1501]]

[[Imported from SVN: r1495]]

[[Imported from SVN: r1494]]

[[Imported from SVN: r1471]]

[[Imported from SVN: r1220]]

[[Imported from SVN: r1206]]

[[Imported from SVN: r1116]]

bugfix: the explicit expression for the Darboux vector given by Dichmann is already in local coordinates

[[Imported from SVN: r1105]]

[[Imported from SVN: r1093]]

[[Imported from SVN: r1092]]

[[Imported from SVN: r1091]]

[[Imported from SVN: r1089]]

[[Imported from SVN: r1088]]

[[Imported from SVN: r1087]]

[[Imported from SVN: r1086]]

[[Imported from SVN: r1073]]