Don't show armor and weapons in the item store if the player already has its next upgrade
Added ArmorTier and WeaponTier
Use ArmorTier and WeaponTier for shops
Add IPurchasableItem interface that shop items and upgrades share
Update test voxel world
Add UpgradeStore dialog
Update ItemStore and add UpgradeStore to HUD
Implement Team Upgrades NPC and let players purchase upgrades