core/assets: add a way to deactivate sprite animation

sonic-boost.love/core/modules/assets/init.lua

@@ -42,6 +42,8 @@ function Assets:new()
   self:clearTileset()
 
   self.images = {}
+
+  self.isActive = true
 end
 
 function Assets:init()
@@ -68,8 +70,10 @@ function Assets:clear()
 end
 
 function Assets:update(dt)
+  if (self.isActive) then
     self:animationsUpdate(dt)
   end
+end
 
 -- SFX et Musique