Support of Ubuntu 18.04 LTS and doc update to OSM-Carto tag 4.10.0

All documentation has been revised to support Ubuntu 18.04 LTS and to conform to openstreetmap-carto tag v4.10.0, commit 529e3f6 performed on Apr 20, 2018.

Added full support of Noto CJK fonts, including note on the need to backport FreeType on Ubuntu 16.04 and method to remove the warning with unifont Medium.

Revised Mapnik compilation procedure and mod_tile configuration.

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