Put order in xbeam_solv.f90:

Notes: 
- the modifications for Spherical joint have been kept in the solver file xbeam_solv (as opposed as in the assembly - this approach was used for the static solver) as the total matrices for the couples system are assembled here, and not in the assembly (which are divided into assembly for structural and rigid body dynamic problems). 
- The BCs are spherical joints but they are labelled as Hflag in the Node type (misleading).
- Possible imporvements have ben listed before before the stop statement in case of non-convergence. these include:
1. old convergence criteria used;
2. delta for generalised coordinates q set to zero for predictor part but not for the corrector part. Hardcoding it to zero would ensure the translational equations at the hinge/sherical joint to be verified.
3. For moving hinge, the zero hardcoding will have to be eliminated and the equations 
dxddt = 0 will have to be substituted with dxdt = 0. Also, the column part of the matrices related to the translational dofs, set to zero to imporve stability, will have to be made non-zero.