Revive Light & Shadow Staffs #246

LightAndShadowResources contains special staffs that are currently not really used within Light & Shadow. This feature request is about improving their value for the game and properly integrating them into it.

The first part of the task is to check whether they generally still work and if not, fix them. Here's a list of assumptions that should be checked:

• Staffs are activated by either of the following: left-click, right-click, E
• On activation, staffs send projectiles based on their type in the targeted direction
• Projectiles are visible and correctly oriented (i.e. not upside down)
• Staff activation has a cool-down and cannot be spammed

The second part of the task is to add effects to the different staffs. Here's a list of different type of effects that can be used, some of which already exist (after being extracted as described in Terasology/Towers#4):

• Fire Effect: Applies damage over time which could spread to other enemies
• Poison Effect: Initially deals a fixed amount of damage and then damages the enemy over time
• Damage Effect: Only damages the enemies
• Ice Effect: Slows down the player
• Stun Effect: Prevents the player from moving for a certain duration of time
• Visual Effect: Makes enemies look larger than they are

Further effects might be introduced by Terasology/CombatSystem#90.

The second part of the task is to properly integrate the staffs into the Light & Shadow gameplay.
This includes adding them as purchasable items to the in-game shop and making sure they are removed from the player inventory when the money is reset on restarting the game after a round ended.

Depends on Terasology/Towers#4