Revised g_tune_pme

Revised g_tune_pme

1. Now, g_tune_pme only duplicates mdrun options where necessary,
options not understood by g_tune_pme are simply passed over to mdrun.
2. Users can now set minimum and maximum Coulomb radius iso scaling
factors for rcoulomb and the Fourier grid.
3. As a result of 1 and 2, some cleanup of the code was possible and
unneeded code was removed.
4. For -npme auto, the tool now derives a reasonable number of PME-
only nodes from the .tpr file settings and tests values around this
number.
Change-Id: I88af5d38a61e0409613f5f3fd4272f7f43823f64