major UIWidget rewrite with new features

modules/core_widgets/uiprogressbar.lua

@@ -0,0 +1,19 @@
+UIProgressBar = extends(UIWidget)
+
+function UIProgressBar.create()
+  local progressbar = UIProgressBar.internalCreate()
+  progressbar:setFocusable(false)
+  progressbar:setPhantom(true)
+  progressbar.percent = 100
+  return progressbar
+end
+
+function UIProgressBar:setPercent(percent)
+  self:setBackgroundHeight(self:getHeight())
+  self:setBackgroundWidth((percent * self:getWidth())/100)
+  self.percent = percent
+end
+
+function UIProgressBar:getPercent()
+  return self.percent
+end