Move Californium to a dedicated GitHub organization

Californium's team is willing to move a dedicated GitHub organization in order to be able to use security advisories.

The current active repos are

• https://github.com/eclipse/californium
• https://github.com/eclipse/californium.tools
• https://github.com/eclipse/californium.actinium

The others, e.g. https://github.com/eclipse/californium.core, https://github.com/eclipse/californium.scandium are not longer maintained.

The team would like to start with a single one https://github.com/eclipse/californium.tools first.

Thanks!