[RTL UI] update widgets and apps for UI mirroring

Small tweaks all around to handle UI mirroring:
- swap existing symbols like arrows, or use alternative ones
- rotate some images, like chevrons and dogear icons
- flip some left and right swipe handling
- flip some geometry arithmetic like tap on left or right
  side of page or dict window
- use new ProgressWidget:getPercentageFromPosition() instead
  of geometry arithmetic
- BD.wrap() some concatenated string bits, like in reader
  and menu footers
- flip inverse_reading_order when UI is mirrored

More specific tweaks:
- ReaderGesture: reset some specific gestures when UI direction
  has changed (tap on top/bottom left/right corners, for
  bookmarks and FileManager "Plus menu").
- ReaderRolling: show markers on the correct side of page,
  in single or dual page mode.
- KoptOptions: swap left and right icons in Alignment toggle
- CheckMark: proper rendering in all 4 mirroring/rtl combinations.
- VirtualKeyboard: forbid any mirroring
- Move util.getMenuText into Menu.lua

frontend/ui/widget/button.lua

@@ -33,6 +33,7 @@ local Button = InputContainer:new{
     text = nil, -- mandatory
     text_func = nil,
     icon = nil,
+    icon_rotation_angle = 0,
     preselect = false,
     callback = nil,
     enabled = true,
@@ -74,6 +75,7 @@ function Button:init()
     else
         self.label_widget = ImageWidget:new{
             file = self.icon,
+            rotation_angle = self.icon_rotation_angle,
             dim = not self.enabled,
             scale_for_dpi = true,
         }