BUGFIX: AMR fixes in multigrid relaxation
Merge pull request #30 from gawrysz/BUGFIX_multigrid_AMR

BUGFIX: AMR fixes in multigrid relaxation
[multigrid_gravity] Implemented automagic convergence check for relaxation (order 2) on coarsest level
[multigrid_gravity] Implemented automagic convergence check for relaxation (order -4) on coarsest level
[multigrid_gravity] corrected messages
[multigrid_gravity] warn if the convergence threshold on coarsest level is not met.
[multigrid_gravity] vhanged default nsmoob
[multigrid_gravity] moved duplicated piece of code to a separate function
[multigrid] cp src/multigrid/multigridvars.F90 src/multigrid/multigrid_helpers.F90
[multigrid] multigridvars provides no subroutines and multigrid_helpers provides no variables
QA
[multigrid] updated comments
Merge pull request #31 from gawrysz/MG_relax_coarsest_convergence

Mg relax coarsest convergence