Change ogs5msh fileio

Following changes are introduced. 
- While reading OGS5 mesh files, keep original order of element node IDs in the file (the order was reversed before)
- While writing OGS5 mesh files, keep original order of element node IDs.
- While writing OGS5 mesh files, output also lines and zero content elements

As pointed out in #180, the node order is same between OGS6 and OGS5 at least for linear order.  There is no need of reversing the ordering. Line elements and zero content elements can be used for some simulations. Hence they should not be automatically excluded from mesh files.