Simplified Backend property files

Removed extra info not actually used
Removed Clipperz Copyright claim to external library files

Removed Clipperz Copyright claim wrongly attached to external library files by the sync script that updated the public repository work area when the changes are committed to the private repository.
Updated Copyright claims

- updated reference dates;
- removed reference to Community Edition;
- normalized logging using Clipperz.log[Warn|Error|Debug]