Revert "fdo#75757: remove inheritance to std::map"

This reverts commit a2deca9d755710bd543fd0caaea0352ac746396d: config_map had
been introduced on purpose with bfb978334cea775b8ae5c40ceea050ea0660d80a
"configmgr: faster / simpler compare for keys."

Change-Id: I3ae0edc4d23977c6537bd2f462f90a702266de6d