Added a missing call to SetLines in the PonyCollection loader that meant most speech was not being used as it had not been categorized.
Fixed bug in CopyTo of ImmutableArray. Made ToImmutableArray method more efficient by returning the source if it is already an ImmutableArray.
Moved some loading into PonyBase class from PonyCollection. Removed MutablePonyBase class (PonyBase was simply not going to be fudged into immutability).

Added some exception handling to make loading of the program more robust in the face of bad file locations given for images.
Changed editor to allow creating a new pony without needing to specify an initial behavior, and also to update thumbnail icon in list when behavior images change.