Various tweaks / enchancements to bonus mechanics

- Added CREATURE_SPELL_POWER for commanders
- Added spell modifiers to various spells: Hypnotize (Astral), Firewall (Luna), Landmine 
- Fixed ENEMY_DEFENCE_REDUCTION, GENERAL_ATTACK_REDUCTION
- Extended usefulness of ONLY_DISTANCE_FIGHT, ONLY_MELEE_FIGHT ranges

git-svn-id: https://vcmi.svn.sourceforge.net/svnroot/vcmi/trunk@3165 4dfc6b2a-8b31-0410-aa91-d6c70e3ac834