Update license to current OGS license.

Closes #2.

LICENSE.txt

-Copyright (c) 2012-2017, OpenGeoSys Community (http://www.opengeosys.org)
+Copyright (c) 2012-2020, OpenGeoSys Community (http://www.opengeosys.org)
 All rights reserved.
 
 Redistribution and use in source and binary forms, with or without
@@ -8,15 +8,9 @@ modification, are permitted provided that the following conditions are met:
 2. Redistributions in binary form must reproduce the above copyright
    notice, this list of conditions and the following disclaimer in the
    documentation and/or other materials provided with the distribution.
-3. All advertising materials mentioning features or use of this software
-   must display the following acknowledgement:
-   This product includes software developed by the OpenGeoSys Community.
-4. Neither the name of the OpenGeoSys Community nor the
+3. Neither the name of the OpenGeoSys Community nor the
    names of its contributors may be used to endorse or promote products
    derived from this software without specific prior written permission.
-5. Attribute the OpenGeoSys Community, preferably citing an appropriate
-   paper listed on the OpenGeoSys Community homepage:
-   http://www.opengeosys.org/papers
 
 THIS SOFTWARE IS PROVIDED BY THE OpenGeoSys Community ''AS IS'' AND ANY
 EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED