Feature Request: Add DC types to NWNX_FEAT_MODIFIER_SPELLSAVEDC

[ID99374836576228]

As per comments, currently NWNX_FEAT_MODIFIER_SPELLSAVEDC only allows global DC modification (i.e. all spells).

Please consider adding some of the following:

• Spell school DC modifiers
• DC modifiers for specific spell levels
• Arcane/Divine DC modifiers
• Individual spells DC modifiers