[1.10] More event hooks and morph "healing" fix

[asanetargoss]

Adds a new event hook for morph ghost spawns, and separates all cancelable events into a Pre-event which can be canceled and a Post-event which occurs only after the corresponding action occurred successfully.

Included also is a fix for a new bug that occurs with ToughAsNails installed and difficulty set to Hard, which only surfaces with the upcoming Forge build (to succeed 12.18.3.2422). With the upcoming Forge build, morphing into a chicken should no longer kill you, however, morphing back into a mob with higher health would result in your HP being reset to full regardless of how much HP you had before you morphed. The fix I have given records the HP ratio that the player had before they morphed, to prevent using morphs to cheese heal.

I can PR these changes to other branches as needed.

[mchorse]

@asanetargoss thanks for this wonderful PR. There are some nice things you've got there! :)

I'll do the rest, because I'm going to work on Metamorph in few several days once I'll publish Aperture.

[mchorse]

I hope you don't mind that I formatted the code to make it look uniform with the rest of repository's code. I also converted event base classes to abstract (specifically AcquireMorpEvent, SpawnMorphEvent and MorphEvent), because there is no sense to create instances of those classes.

[asanetargoss]

Perfect! Thank you. :D

No worries about the changes. I expect that from a pull request and am glad you have adjusted them to suit your work. Yea, the base events I wasn't sure about; I was trying to match with Forge's conventions but definitely agree that instantiating those events doesn't make sense.