Add ammo boxes (#325)

Same as magazines except they can't be loaded into a weapon.
You can transfer ammo to and from magazines / boxes freely where the caliber matches so you don't need to necessarily match the magazine type.
Used popups to reflect transfer amount.
Also fixed the mag sprite showing as 0 capacity on spawn and the 10mm smg flash magazine prototype

Content.Client/EntryPoint.cs

@@ -43,6 +43,7 @@ namespace Content.Client
 
             var registerIgnore = new[]
             {
+                "AmmoBox",
                 "Breakable",
                 "Pickaxe",
                 "Interactable",