Code modernization (localisation_util, gateway_util, rhodyn, dkh_old_util)

In this batch: localisation_util, gateway_util, rhodyn, dkh_old_util.

See the wiki.

@kinetik161 Changes in Rhodyn are mostly of style, but since there is no test I may have made some mistake.

• Documentation updated or not needed.
• Test created or not needed.
• Attribution in source files and CONTRIBUTORS.md updated if necessary.