Hippocamps and Horse Equipment Working

Horseshoes, horse armor, and most other horse equipment is working on the 1.15 port of the Ultimate Unicorn Mod, and the horse inventory dialog has most of its functionality back now.  The /changeHorse command works now, too.  Hippocamps can swim again, too!  Once I get the models all looking right I'll make a release, even though some of the features won't be ported.  Then I'll look into porting to 1.16.