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/apps/reader/readerui.lua

@@ -52,11 +52,6 @@ local T = require("ffi/util").template
 
 local ReaderUI = InputContainer:new{
     name = "ReaderUI",
-
-    key_events = {
-        Close = { { "Home" },
-            doc = "close document", event = "Close" },
-    },
     active_widgets = {},
 
     -- if we have a parent container, it must be referenced for now
@@ -97,14 +92,17 @@ function ReaderUI:init()
         self.dialog = self
     end
 
-    if Device:hasKeys() then
-        self.key_events.Back = {
-            { "Back" }, doc = "close document",
-            event = "Close" }
-    end
-
     self.doc_settings = DocSettings:open(self.document.file)
 
+    if Device:hasKeys() then
+        self.key_events.Home = { {"Home"}, doc = "open file browser" }
+        if Device:isSDL() then
+            --if in the desktop emulator
+            --add the old Back key to exit koreader
+            self.key_events.Close = { {"Back"}, doc = "Exit koreader" }
+        end
+    end
+
     -- a view container (so it must be child #1!)
     -- all paintable widgets need to be a child of reader view
     self:registerModule("view", ReaderView:new{
@@ -622,4 +620,8 @@ function ReaderUI:dealWithLoadDocumentFailure()
     error("crengine failed recognizing or parsing this file: unsupported or invalid document")
 end
 
+function ReaderUI:onHome()
+    return self:showFileManager()
+end
+
 return ReaderUI