[S2GRAPH-157]: Check proper apache license header on all files for release 0.2.0
[S2GRAPH-157]: Check proper apache license header on all files for release 0.2.0

JIRA:
    [S2GRAPH-157] https://issues.apache.org/jira/browse/S2GRAPH-157

Pull Request:
    Closes #116

Author
    DO YUNG YOON <steamshon@apache.org>

SteamShon/incubator-s2graph,SteamShon/incubator-s2graph,SteamShon/incubator-s2graph