fix: make mbtiles support optional
fix: make mbtiles support optional

SQLite pulled in by @mapbox/mbtiles is very heavy to
install, so make it optional and log a message if it is
needed for mbtiles charts support.

SignalK/signalk-server-node,SignalK/signalk-server-node,webmasterkai/signalk-server-node,sbender9/signalk-server-node,SignalK/signalk-server-node,sbender9/signalk-server-node,sbender9/signalk-server-node,webmasterkai/signalk-server-node,SignalK/signalk-server-node,webmasterkai/signalk-server-node