add_MARBL (compute): add forcing / initial condition files to INPUTDATA

[mnlevy1981]

Currently, the MARBL_tracers module uses CESM_INPUTDIR='/glade/work/mlevy/cesm_inputdata' to look for inputdata. This is useful since we are making many copies of various input files while debugging the driver, but once we have finalized the inputdata it all needs to be moved to $CESMDATAROOT and imported into the repo.

Keith suggests running a test on izumi prior to merging onto dev/ncar to verify all the data is available.