Redraw spells widget when attuneation changes.
Introduce new header file, common.h, for sharing definitions/calculations/macros/etc between client and server.
Move PATH_SP_MULT and PATH_DMG_MULT macros from server's spells.h to common.h.
Adjust shown spell cost by player's attuneation.
Do not modify calculated spell cost with path attuneation if a specific caster level was requested.
Fix #56: Charisma/wisdom equipment