Kindle4NT improvements (#3745)

* [device][kindle4] add fake event to kindle4

* modify focusmanager to allow for more complex layout

The focusmanager now naviguate the layout by avoiding nil value
instead of relying on table lenght. It should be completely backward
compatible

* add Dpad naviguation to the touchmenu

* fix crash because virtualkeyboard on non touch device

the kindle4NT has no keyboard nor touch, the fix open the virtual
keyboard so koreader dont crash but it's not useable

* Enable device with keys to use the touchmenu

* Don't get stuck in reader progress statistics plugin

* [underlinecontainer] Fix and remove unused function

References #1898.

frontend/ui/widget/iconbutton.lua

@@ -124,4 +124,19 @@ function IconButton:onHoldIconButton()
     return true
 end
 
+function IconButton:onFocus()
+    --quick and dirty, need better way to show focus
+    self.image.invert=true
+    return true
+end
+
+function IconButton:onUnfocus()
+    self.image.invert=false
+    return true
+end
+
+function IconButton:onTapSelect()
+    self:onTapIconButton()
+end
+
 return IconButton