Edit and Clean non-functional files

[destogl]

This sits on top of #66 therefore merge against this branch to see the changes. This can be reviewed before and I will than rebase when #66 is merged.

Goals:

• Clean CMakeLists.txt files
• use Apache 2.0 license in all packages (this is mostly compatible with BSD used before in one package)
• edit authors and maintainers lists
• Add one license file and Contribution guidelines.

[destogl]

Became part of #71.