Iron's Spells 'n Spellbooks Dynamic Skill Trees

This update should be the last one for a while! Changed a few things that I've been testing for a bit:

• Changed the cost of the "Reset" skills to be free (not sure why I didn't do that earlier)
• Added tooltip in "Magic II" to clarify cost of each skill
• Reworked experience progression to be fit for both a grind-y and a more casual gameplay
• Detailed explanation regarding the above will be added to the mod's page description!
• Added Icon to the project (for the Modlist in Minecraft)

Note that when you'll update to this version you might see a slight boost in your levels (particularly for the first tier) due to the slightly lower requirements!