[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/scrollhtmlwidget.lua

@@ -2,6 +2,7 @@
 HTML widget with vertical scroll bar.
 --]]
 
+local BD = require("ui/bidi")
 local Device = require("device")
 local HtmlBoxWidget = require("ui/widget/htmlboxwidget")
 local Geom = require("ui/geometry")
@@ -143,7 +144,7 @@ function ScrollHtmlWidget:onScrollText(arg, ges)
 end
 
 function ScrollHtmlWidget:onTapScrollText(arg, ges)
-    if ges.pos.x < Screen:getWidth()/2 then
+    if BD.flipIfMirroredUILayout(ges.pos.x < Screen:getWidth()/2) then
         if self.htmlbox_widget.page_number > 1 then
             self:scrollText(-1)
             return true