Dump counters are no global variables anymore

 - iseismo, isnap and istrain are now local variables set in sf_time_loop_newmark and symplectic_time_loop and passed down into the dump routines. That should make everything a bit easier to debug.
 - Removed several VERY outdated routines used to dump the wavefield into ASCII files. They would probably not have worked anymore anyway.
Dump timestep zero as well

 - True for all three dump types (seismograms, xdmf/vtk and kernel dumps)
Merge branch 'master' of https://github.com/geodynamics/axisem