Update planelog2sav scripts for SEAC4RS

Updated planelog2sav scripts to take into account that we have two files
for each date because the runs start/end at 2100. One of these files is
filled with junk values before 2100, so we have to deal with this here.

Signed-off-by: Jenny Fisher <jennyf@uow.edu.au>
Updated flightdates in seac4rs_model_merge
Update filename style in make_planeflight (changed for some reason)
Update merge scripts for ER2
New flight files
Remove ARCTAS versions of scripts

The plotscripts_ARCTAS/ directory was causing trouble if you tried to
use the same-named routines from a different directory. I've removed them.
You can still see them at:
/home/jaf/data/ARCTAS/IDL/comparisons/

Signed-off-by: Jenny Fisher <jennyf@uow.edu.au>
Update get_field_data_seac4rs with some ER-2 names.
Make flightdate a keyword in ts_date to match other routines.