[Android] Implement the http authentication in xwalk default client.

The implemented are to provide the http anthentication
funtions to support the necessary requirement of some
web site (e.g. http://mcgwiki.intel.com), covering the
following:
1 Implement the class of HttpAuthDatabase.
2 Initialize the instance of HttpAuthDatabase.
3 Implement the method of setHttpAuthUsernamePassword()
  via the sqlite database to set the username and password.
4 Implement the method of getHttpAuthUsernamePassword().
  via the sqlite database to query the username and password.

BUG=#784, #787