Change license to BSD-3-Clause ("Modified BSD License").

[bilke]

To be discussed...

BSD-3-Clause is an approved OSI license.

• https://opensource.org/licenses/BSD-3-Clause
• https://en.wikipedia.org/wiki/BSD_licenses

1. Feature description was added to the changelog
2. Add citing instructions to web site

[TomFischer]

Why do you want to change the license? In the current version I especially like the point:
Attribute the OpenGeoSys Community, preferably citing an appropriate
paper listed on the OpenGeoSys Community homepage:
http://www.opengeosys.org/papers
Maybe it is important to have such a point in the license to remind other people to reference us. As we have seen in the past this is sometimes necessary. And if such arguments fall on deaf ears we have the license as a solid argument.

[bilke]

At the moment our license does not qualify for a "real" open-source license. A solid argument will still not convince people.. People who are willing to cite us will do so, people who are not will not do so, no matter what license we have (in my opinion).

This PR is also a discussion point on the agenda for the dev meeting on next Tuesday.

[bilke]

All OGS code contributors have agreed to the license change.

[ogsbot]

OpenGeoSys development has been moved to GitLab.

See this pull request on GitLab.