[API][WIN] "position": "mouse" support on Windows. Fix #528.
[API] Support for desktop keyboard hot key. Part of #200.

1. Add method registerGlobalHotkey and unregisterGlobalHotkey in gui.App.
2. Hotkey object implementation both js and C++ code.
3. The implementation on Windows.
[API][GTK] Use Xlib to implement global hotkey. Part of #200.

1. Use XGrabKey and XUngrabKey to implement global hotkey.
2. Refactor the code for better cross-platform.
[API][WIN] Move the HotKeyHandler to the hotkey_handler_win.cc. Part of #200.
[API] Change activated envent to keydown, and add keyup event on Linux. Part of #200.
[API][GTK] Keep consistency withe windows platform.

If a hot key has been registered in current app, the second one with same key
conbination should be failed.
[GTK] Add error handler to prevent the process from exiting.
[API] Add key attribute for HotKey object.
Fix typo.
[Test] Manual and automatic test case for HotKey.
[test] automatic test case for console.log
[test] fix test case for console.log
[README] update for 0.6.2
Merge pull request #849 from kingFighter/tests

[test] automatic test case for console.log
[test] update console.log
autotest for user agent when creating a new app
Merge pull request #853 from richardcypher/tests

autotest for user agent when creating a new app
add test case for the data-path argument for chromium args
add test case for the data-path argument for chromium args
undo the change in package.json