Standardized LICENSE text to BSD-3-Clause

[kvrigor]

Current LICENSE file is based from GitHub's BSD-3 license template. It would be better to use a LICENSE text from a more authoritative source: https://opensource.org/license/BSD-3-Clause. Other references:

• BSD-3-Clause (SPDX.org)
• BSD-3-Clause (ChooseALicense.com)
• 3-clause license (Wikipedia)

This PR also fixes #134.

[jjokella]

To me, the "legal content" of the license is not changed, so that should be fine. Others have to check that the citation style/authors etc is correct, but from my side this is good.

[s-poll]

I believe that, from a legal point of view, the PR is a change to the licence. It is these legal subtleties that could prove problematic. IMO, it might important here not to change the licence of CLM (CTSM). It might be possible to introduce a separate licence by using two licences, as it is also used at different repos. As having only a superficial understanding of licences can be dangerous, I would suggest that we ask the legal department to clarify this. There is certainly somebody at JSC/FZJ.

[s-poll]

Isn't this a change in license?

[kvrigor]

It is these legal subtleties that could prove problematic. IMO, it might important here not to change the licence of CLM (CTSM).

There should be no legal problems since we're not customizing our LICENSE and simply adhere to a standard BSD-3 LICENSE file (links in my 1st post). The original CTSM LICENSE is based from GitHub's BSD-3 license template; what I did is to replace the text with more authoritative source and clearly specify that it's a BSD-3-Clause LICENSE.