Added two new neutral creeps with unique attack mechanisms

Added two new neutral creeps with unique attack mechanisms:

Shaman: 

Ranged Attack. Absorb the enemy's defense or experience points and converts them into its own vitality.

Bone Thrower: 

Ranged Attack. Average Knockback. Healing skeleton warrior: When thrown bone touches a skeleton warrior, no matter if the skeleton warrior is on our side or the enemy side, it will be healed... and the bone can make the skeleton warrior's lost bones grow back (restore to the state before losing the first life)

Redrawn some maps to be more interesting.