Raise MemoryError proactively in certain cases

[dbetchkal]

In NMSIM_InputOutputTools.tbx, it seems appropriate to anticipate that some users may try to create projects so large that NMSIM will crash. This should be handled in advance.

There are two prerequisites:

1. What is NMSIM's memory limit? (Presumably constant.) Convert to a maximum area.
2. How to extract the area of the Study Area Polygon from the Attribute Table using SearchCursor? Should be pretty easy.

[chevelle3504speed]

Additionally, if modeling slow-moving sources such as ATVs and ORVs, the speed of the vehicle and length of trail/trajectory appear to have sizeable effects on software memory limitations. If NMSim crashes when attempting to generate an output (.tig) file, create a new trajectory file and increase vehicle speed and/or reduce length of trail/path to be modeled before reattempting output file generation. Speeds of <8 mph have been problematic on path/trajectories 18 km long in early testing.