move hooks subdirectory under Kea own directory

Please consider moving Kea hooks directory on Linux installations from /usr/lib/hooks to /usr/lib/kea/hooks or /usr/libexec/kea/hooks. The directory /usr/lib/hooks is not connected to Kea in any sense and putting Kea files into it make mess. According to FHS (Filesystem Hierarchy Standard) referenced in LSB (Linux Standard Base, ISO 23360), software should put its extra files like binaries and libraries under these directories.