classes: add maxMP to statsComputed [https://github.com/HabitRPG/habitrpg/issues/1994]
classes: replenish 10MP on cron
classes: charge gems for change-class
classes: add .3*PER to chanceMultiplier in drops. Add .5+(.05*STR) to
crits (.03 chance) This is a temporary until we get all the numbers worked out. @SabreCat
classes: fixes & balancing of spells
[https://github.com/HabitRPG/habitrpg/issues/1994] fix TigerCub not appearing
[https://github.com/HabitRPG/habitrpg/issues/1994] fixes to purchasing shirts