after an app is minimized, the app icon does not respond when you click
the app icon on the Desktop

solve the problem of the application window can be drawn as a line.
resloved the WeChat button overlapping problem.

solve code style problem in window module.

1.call a virtual function in dtor will always get 0.
  so we can never destroy native_window_. adjust native_window_
  to /wm/window.h can solve this issue.
2.delete icon after SDL_SetWindowIcon, which is what SDL tell us
  to do in the official SDL documents.

continuously maximize window will crash some app, such as qqmusic...

Add four window property:
  HIDE_BACK
  HIDE_CLOSE
  HIDE_MAXIMIZE
  HIDE_MINIMIZE

set qqmusic HIDE_BACK

note: if you change window property on anbox, you should change it on android at the same time.
change file on android: frameworks/base/core/java/com/android/internal/widget/DecorCaptionView.java

Some app opens in horizontal screen, but window on anbox side is in vertical state,
As the result, bottom of the window has black area.
To solve this problem, we adjust window on anbox side when app opens in horizontal
screen state.
But, when window adjusted by user, app follows this adjustment and send
this adjustment to anbox at the second time. So change of this commit has no effect
after window is adjusted by user or 15s timeout.

While left button down, calculate the point of down event.
--If in minimium button area, minimize window as result.
--If in back button area, send BACK event to android-framework.
Note: This commit code is just to do button function, button Appearance code is in android-framework.

This implements client side window decorations of our windows. The title
bar of our windows is now drawn by Android and we simply map out the
title bar area hit test area to SDL to detect when the other wants to
move the window or resize it.

For debugging and development purposes it's sometimes useful to run the
full Android system in a single and statically sized window. This is not
going to be a widely used mode but can be helpful at times.

Also makes our window/layer management a bit more modular to allow easy
additions of new strategies/impementations.

This leads to much better performance and user interaction. Resizing
still has some flickering but that is a different area of problems.

Currently not working as Unity8 does not provide pointer input
events yet.