[Android] Embedding API 3.0: XWalkPreferences

Add following APIs:
public static final String JAVASCRIPT_CAN_OPEN_WINDOW;
public static final String ALLOW_UNIVERSAL_ACCESS_FROM_FILE;
public static final String SUPPORT_MULTIPLE_WINDOWS
public static void setValue(String key, String value);
public static void setValue(String key, int value);
public static boolean getBooleanValue(String key);
public static String getStringValue(String key);
public static int getIntegerValue(String key);

Deprecated API:
public static boolean getValue(String key);

BUG=https://crosswalk-project.org/jira/browse/XWALK-2376
Merge pull request #2354 from wang16/embedding_api_3

[Android] Embedding API 3.0: XWalkPreferences