Remove hardcoded loading

Changes in UI script:
- Added a new function: `loadingGetProgress` - Returns a percentage of loaded assets during the game loading.
- Removed the hardcoded progress bar update and the button appearing.
  - Add the following code instead, to the `tick` callback:
  ```
  -- update splash screen
  local splash = f.getWidgetN("splash/Main")
  if splash then
    local progress = f.loadingGetProgress()
    f.getWidgetN("splash/Main/Frame/Progress").widget.valueData = progress
    if progress == 1 then
      f.getWidgetN("splash/Main/Frame/Button_Play"):show()
    end
  end
  ```

src/UI/Manager.lua

@@ -17,6 +17,7 @@ function UIManager:new()
   self.scriptFunctions = {
     loadMain = function() _Game:loadMain() end,
     initSession = function() _Game:initSession() end,
+    loadingGetProgress = function() return _Game.resourceManager.stepLoadProcessedObjs / _Game.resourceManager.stepLoadTotalObjs end,
 
     levelStart = function() _Game.session:startLevel() end,
     levelBegin = function() _Game.session.level:begin() end,
@@ -117,16 +118,6 @@ function UIManager:update(dt)
 		end
 	end
 
-	-- TODO: HARDCODED - make it more flexible
-	if self.widgets.splash then
-		-- splash progress bar
-		self.widgets.splash.children.Frame.children.Progress.widget.valueData = _Game.resourceManager.stepLoadProcessedObjs / _Game.resourceManager.stepLoadTotalObjs
-		-- splash play button
-		if self.widgets.splash.children.Frame.children.Progress.widget.value == 1 then
-			self.widgets.splash.children.Frame.children.Button_Play:show()
-		end
-	end
-
 	for widgetN, widget in pairs(self.widgets) do
 		widget:update(dt)
 	end

src/UI/Widget.lua

@@ -126,7 +126,7 @@ function UIWidget:update(dt)
 			-- instead, you need to clean up the black background manually!
 		end
 	end
-	if self.time and (not self.parent or self.parent:isVisible()) then
+	if self.time then
 		self.time = self.time - dt
 		if self.time <= 0 then
 			self.time = nil