Adding regrid to_grid configuration for all MET tools that have it

[georgemccabe]

Currently only PointStat has this config option. Other tools should have this support as well.

[georgemccabe]

This has been implemented for all wrappers that have a regrid to_grid option (GridStat, MODE, MTD, EnsembleStat, SeriesBy*). I cleaned up the set_environment_variables function to make it easier to add new commonly used environment variables and print out list of environment variables that were set by the wrapper (no longer have to keep track of list of items, self.add_env_var adds to a list automatically and print function uses that list). Added documentation for each new config variable <APP_NAME>_REGRID_TO_GRID.