Magazine reloading

[snipercup]

This requires #60 to work. I will publish this PR as a draft to make sure #60 gets merged first.

You can now run out of bullets

• Changed the relationship between the equippedItem and the Equipmentslot. EquippedItem will handle firing and managing the reload constraints. EquipmentSlot will interact with the inventory to manage the magazines
• Added the "current_ammo" property as an editable field in the magazine editor. In the future we might specify a range here to create half-spent magazines
• Magazines are removed from the inventory and stored in the equipmentslot while they are inside the weapon. When a reload happens, the current magazine is added to the inventory and a different one will be loaded into the weapon (equipmentslot)
• When reloading, the magazine in the player inventory with the most bullets is chosen
• The player can drop a magazine from the inventory onto the gun to reload it with that specific magazine
• When an item is unequipped, the magazine is also returned to the inventory. Right now the only way to have a loaded weapon is to equip it and then reload it.
• Made the action timer and handling more generic. We can now pass a function to General with a time duration and it will call that function when the time runs out. It will also enforce that only one action is executed at a time