Added check at end of step for adding transport

At the end of each drifter loop, a 2D check has been added such that each time a drifter hits a horizontal grid cell wall, that drifter's initial volume transport is added and subtracted from the two relevant cells. This is a start to integrating functionality for calculating Lagrangian stream functions.
Updated run.py call for optional stream arguments
added dostream to run and step
More steps for being able to run stream functions
fixed up dostream call to step
setup for lagrangian stream functions as option
Trying to fix bug with using stream function

Changed idrift to adjust according to how many drifters have exited the domain
Trying to get U0,V0 working
Eliminated idrift since I don't think I need it
Trying to fix call using U0, V0

U0, V0 may not have properly been accounting for drifters that have exited the domain.
changed save a little for Urho/Vrho
another attempt at stream functions
forgot to comment things out
Background plotting change via grid

Now parameters can be input to readgrid in inout in order to choose the size of the basemap for plotting magnifications of the shelf model.
update to calculation of volume transport on grid

I had previously been thinking about the movement of drifters across the grid cells on a cell by cell basis, and how drifters move between cells. I think this was a bit wrong and I have updated the code so that it is on a grid cell wall basis, and it is examined where drifters go by wall and in what direction.
had to comment out some set_traces
Changes to size of volume transport arrays

Changed all Urho and Vrho to U and V since not on the rho grid anymore. Also had to update the size declaration in step.f95 accordingly.
more name changes I missed
switched order of dimensions in savetracks
had to updated more sizes and change to ut,vt