Add horizontal_padding to IconButton (#3213)

TouchMenu (top menu) and ConfigDialog (bottom menu) updated
to make use of that. This provides a wider sensitivity to
menu buttons.

frontend/ui/widget/iconbutton.lua

@@ -2,6 +2,8 @@
 Button with a big icon image! Designed for touch devices.
 --]]
 
+local HorizontalGroup = require("ui/widget/horizontalgroup")
+local HorizontalSpan = require("ui/widget/horizontalspan")
 local InputContainer = require("ui/widget/container/inputcontainer")
 local ImageWidget = require("ui/widget/imagewidget")
 local GestureRange = require("ui/gesturerange")
@@ -13,6 +15,7 @@ local IconButton = InputContainer:new{
     -- show_parent is used for UIManager:setDirty, so we can trigger repaint
     show_parent = nil,
     scale_for_dpi = true,
+    horizontal_padding = 0,
     callback = function() end,
 }
 
@@ -23,11 +26,27 @@ function IconButton:init()
     }
 
     self.show_parent = self.show_parent or self
+
+    self.button = HorizontalGroup:new{}
+    table.insert(self.button, HorizontalSpan:new{})
+    table.insert(self.button, self.image)
+    table.insert(self.button, HorizontalSpan:new{})
+
+    self[1] = self.button
+    self:update()
+end
+
+function IconButton:update()
+    self.button[1].width = self.horizontal_padding
+    self.button[3].width = self.horizontal_padding
     self.dimen = self.image:getSize()
-
+    self.dimen.w = self.dimen.w + 2*self.horizontal_padding
     self:initGesListener()
+end
 
-    self[1] = self.image
+function IconButton:setHorizontalPadding(padding)
+    self.horizontal_padding = padding
+    self:update()
 end
 
 function IconButton:initGesListener()