Add API to access battery power state

Done:
- X11, server (tested)
- Windows (developed, would be nice to retest)
- OSX (not tested)
Prepared (not developed):
- Android (code is here, but may not compile)
- iphone
- winrt
- bb10
- haiku
- javascript

platform/javascript/power_javascript.h

@@ -0,0 +1,51 @@
+/*************************************************************************/
+/*  power_javascript.h                                                   */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                    http://www.godotengine.org                         */
+/*************************************************************************/
+/* Copyright (c) 2007-2016 Juan Linietsky, Ariel Manzur.                 */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+
+#ifndef PLATFORM_JAVASCRIPT_POWER_JAVASCRIPT_H_
+#define PLATFORM_JAVASCRIPT_POWER_JAVASCRIPT_H_
+
+class PowerJavascript {
+private:
+	int nsecs_left;
+	int percent_left;
+	PowerState power_state;
+
+	bool UpdatePowerInfo();
+
+public:
+	PowerJavascript();
+	virtual ~PowerJavascript();
+
+	PowerState get_power_state();
+	int get_power_seconds_left();
+	int get_power_percent_left();
+};
+
+#endif /* PLATFORM_JAVASCRIPT_POWER_JAVASCRIPT_H_ */