Fixes off-by-one data errors in the spaceport animations file. Animation
cel images have a directory entry, specifying their size (in byes) and
location (offset) in the file, as well as a header with width & height
prior the pixel data. The width value was frequently off by one. This
corrects the file, and removes the fix which had been added to the code.

Break the massive SpotActivity function into component functions. Rename
variables so their purpose is clear.

Replace hardcoded indices used in spaceport animations with an
enumeration. Also moved animation selection code to separate functions
for clarity.