Refactoring hardware abstraction

This is a major overhaul of the hardware abstraction layer.
A few notes:

General platform distinction happens in
  frontend/device.lua
which will delegate everything else to
  frontend/device/<platform_name>/device.lua
which should extend
  frontend/device/generic/device.lua

Screen handling is implemented in
  frontend/device/screen.lua
which includes the *functionality* to support device specifics.
Actually setting up the device specific functionality, however,
is done in the device specific setup code in the relevant
device.lua file.

The same goes for input handling.

reader.lua

@@ -30,45 +30,23 @@ end
 
 local lfs = require("libs/libkoreader-lfs")
 local UIManager = require("ui/uimanager")
-local Device = require("ui/device")
-local Screen = require("ui/screen")
+local Device = require("device")
+local Screen = require("device").screen
 local input = require("ffi/input")
 local DEBUG = require("dbg")
 
 local Profiler = nil
 
 local function exitReader()
-    local KindlePowerD = require("ui/device/kindlepowerd")
     local ReaderActivityIndicator = require("apps/reader/modules/readeractivityindicator")
 
     G_reader_settings:close()
 
     -- Close lipc handles
-    KindlePowerD:coda()
     ReaderActivityIndicator:coda()
 
-    if not util.isEmulated() then
-        if Device:isKindle3() or (Device:getModel() == "KindleDXG") then
-            -- send double menu key press events to trigger screen refresh
-            os.execute("echo 'send 139' > /proc/keypad;echo 'send 139' > /proc/keypad")
-        end
-        if Device:isTouchDevice() and Device.survive_screen_saver then
-            -- If needed, hack the swipe to unlock screen
-            if Device:isSpecialOffers() then
-                local dev = Device:getTouchInputDev()
-                if dev then
-                    local width, height = Screen:getWidth(), Screen:getHeight()
-                    input.fakeTapInput(dev,
-                        math.min(width, height)/2,
-                        math.max(width, height)-30
-                    )
-                end
-            end
-        end
-    end
-
-    input.closeAll()
-    Screen:close()
+    -- shutdown hardware abstraction
+    Device:exit()
 
     if Profiler then Profiler.stop() end
     os.exit(0)