aggiunta icona bazooka + refactoring icone seguendo i canoni di Minetest

_weapons/bazooka.lua

@@ -4,7 +4,7 @@ quake.register_weapon("quake:bazooka", {
   mesh = "bazooka.obj",
   tiles = {"quake_bazooka.png"},
   wield_scale = {x=1.3, y=1.3, z=1.3},
-  inventory_image = "railgun.png",
+  inventory_image = "quake_bazooka_icon.png",
   weap_damage = 10,        --FF7 in my heart
   weap_delay = 0.8,
   weap_sound_shooting = "quake_railgun_shoot",

_weapons/railgun.lua

@@ -4,7 +4,7 @@ quake.register_weapon("quake:railgun", {
   mesh = "railgun.obj",
   tiles = {"quake_railgun.png"},
   wield_scale = {x=1.3, y=1.3, z=1.3},
-  inventory_image = "railgun.png",
+  inventory_image = "quake_railgun_icon.png",
 
   weap_damage = 777,        --FF7 in my heart
   weap_delay = 0.8,

_weapons/shotgun.lua

@@ -4,7 +4,7 @@ quake.register_weapon("quake:shotgun", {
   mesh = "railgun.obj",
   tiles = {"quake_railgun.png"},
   wield_scale = {x=1.3, y=1.3, z=1.3},
-  inventory_image = "shotgun.png",
+  inventory_image = "quake_shotgun_icon.png",
 
   weap_damage = 10,
   weap_delay = 0.8,