fix a potential crash related to loading effects

fix a potential crash related to loading effects

• fixed a potential crash with iron's spells 'n spellbooks
• added optional show_icon field for effect rewards

• added effect reward from newer versions (incl. a new field show_icon, which is used by the grant type to show the icon in the gui)
• made iron's spells an optional dependency
• fixed a compatibility issue with the newest puffish skills version
• adjusted debug logging for spell cast experience source

adjusted effect reward behaviour

• amplifier of infinite duration effects are now properly modified
• if the amplifier goes below 0 or the duration reaches 0 (or goes below 0) the effect will not be applied