Updates by Will

Adding numerous modifications by Will Hobbs, plus one additional file for
creating cumulative graphs of loads by land use.
Fixed error, new outputs

Fixed an error in Load_byParam_sub2_AssignCase.R, which occurred when
attempting to graph parameters for which no data existed.  Also switched
some graphing in the same script to output PNG, rather than PDF.
Select instead of list in webpage

Converted the parameter filter from a list to a select box.  Still have an
issue with having the right one selected on load; otherwise working.
PNG output for two scripts

Resolved issues with margins (put png() statement before par() statement
updating the margins), and created (default) option for png output.