More chart sources

[Skippern]

Try to integrate more map sources. Check out further lists of possible sources:

• https://sites.google.com/site/nauticalfree
• http://opencpn.org/ocpn/chart_sources
• http://ec2-54-235-76-27.compute-1.amazonaws.com/ienc/web/main/ienc_009.cfm
• http://scsenc.eahc.asia/main.php
• http://www.antarescharts.co.uk/
• https://www.openseachart.org/doku.php/rnc