Radius corners of more boxes (#6997)

This gives a more uniform look than having some boxes rectangular and some
with radiused corners

frontend/ui/widget/confirmbox.lua

@@ -136,6 +136,7 @@ function ConfirmBox:init()
     local frame = FrameContainer:new{
         background = Blitbuffer.COLOR_WHITE,
         margin = self.margin,
+        radius = Size.radius.window,
         padding = self.padding,
         padding_bottom = 0, -- no padding below buttontable
         VerticalGroup:new{

frontend/ui/widget/infomessage.lua

@@ -145,6 +145,7 @@ function InfoMessage:init()
     end
     local frame = FrameContainer:new{
         background = Blitbuffer.COLOR_WHITE,
+        radius = Size.radius.window,
         HorizontalGroup:new{
             align = "center",
             image_widget,

frontend/ui/widget/multiconfirmbox.lua

@@ -134,6 +134,7 @@ function MultiConfirmBox:init()
             FrameContainer:new{
                 background = Blitbuffer.COLOR_WHITE,
                 margin = self.margin,
+                radius = Size.radius.window,
                 padding = self.padding,
                 padding_bottom = 0, -- no padding below buttontable
                 VerticalGroup:new{