Draft: Switch to vector tiles

This is very much work in progress and in the meantime only open for evaluation purposes.

conf/all-buildings/renderd.conf

-[renderd]
-stats_file=/run/renderd/renderd.stats
-socketname=/run/renderd/renderd.sock
-num_threads=4
-tile_dir=/var/cache/renderd/tiles
-
-[mapnik]
-plugins_dir=/usr/lib/mapnik/3.0/input
-font_dir=/usr/share/fonts/truetype
-font_dir_recurse=true
-
-[all-buildings]
-URI=/all-buildings
-XML=/srv/mapnik/obm-all-buildings.xml