Update ED2 licence

[mpaiao]

Description

The previous licence (CC-BY-4.0) turns out not to be ideal for softwares.

My suggestion is to go with GNU GPLv3, which is rather permissive, with the only exception being that no one can make derivative work with ED2 and put it in closed software. If anyone sees this as a problem, or is more versed in licences than I am, please let me know your thoughts on it.

I am making this PR a draft one because if we go with GNU GPLv3, we may want to go through every file and add the suggestions listed at the end of the licence itself. I am happy to do it if people are onboard with it.

Collaborators

Types of changes

• Hot fix (emergential bug fix to make ED2 run again)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Other (fix or feature that would cause existing functionality to change)

Changes in Settings, Input Files or Output Files

• This feature requires changes in ED2IN
• This feature requires changes in the XML parameter file
• This feature requires changes in other input files
• This feature will change output files

Expectation of Answer Changes:

• No changes expected (bit-for-bit compatibility)
• Changes expected with specific configurations (see details below)
• Changes expected in all simulations (see details below)

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• ED2 Wiki update:

Testing :

• All new and existing tests passed.