Reimplement text edit scrolling in C++

* And update some corelib APIs

modules/corelib/ui/uispinbox.lua

@@ -3,11 +3,14 @@ UISpinBox = extends(UITextEdit)
 
 function UISpinBox.create()
   local spinbox = UISpinBox.internalCreate()
+  spinbox:setFocusable(false)
   spinbox:setValidCharacters('0123456789')
   spinbox.displayButtons = true
   spinbox.minimum = 0
   spinbox.maximum = 0
   spinbox.value = 0
+  spinbox.step = 1
+  spinbox.firstchange = true
   spinbox:setText("0")
   return spinbox
 end
@@ -21,6 +24,14 @@ function UISpinBox:onMouseWheel(mousePos, direction)
   return true
 end
 
+function UISpinBox:onKeyPress()
+  if self.firstchange then
+    self.firstchange = false
+    self:setText('')
+  end
+  return false
+end
+
 function UISpinBox:onTextChange(text, oldText)
   if text:len() == 0 then
     self:setValue(self.minimum)
@@ -79,14 +90,15 @@ function UISpinBox:hideButtons()
 end
 
 function UISpinBox:up()
-  self:setValue(self.value + 1)
+  self:setValue(self.value + self.step)
 end
 
 function UISpinBox:down()
-  self:setValue(self.value - 1)
+  self:setValue(self.value - self.step)
 end
 
 function UISpinBox:setValue(value)
+  value = value or 0
   value = math.max(math.min(self.maximum, value), self.minimum)
   if value == self.value then return end
   if self:getText():len() > 0 then
@@ -107,6 +119,7 @@ function UISpinBox:setValue(value)
 end
 
 function UISpinBox:setMinimum(minimum)
+  minimum = minimum or -9223372036854775808
   self.minimum = minimum
   if self.minimum > self.maximum then
     self.maximum = self.minimum
@@ -117,12 +130,17 @@ function UISpinBox:setMinimum(minimum)
 end
 
 function UISpinBox:setMaximum(maximum)
+  maximum = maximum or 9223372036854775807
   self.maximum = maximum
   if self.value > maximum then
     self:setValue(maximum)
   end
 end
 
+function UISpinBox:setStep(step)
+  self.step = step or 1
+end
+
 function UISpinBox:getValue()
   return self.value
 end