City Canal Rework

Removes the canal graphic in directly coastal cities. Coastal city centers often show a canal graphic where it's sometimes undesirable and out of place. This mod removes the graphic and only shows it when necessary. Occasionally the canal graphic can be a helpful or needed indicator for some mechanics, this mod allows a few of those exemptions where showing the graphic (i.e. not removed) makes sense. The first exemption is when a city is adjacent to a canal district, that city should, of course, show the graphic to link both canals. Second, if the city is founded on a tile connecting two bodies of water, the graphic should be shown to indicate that that city is a Canal City, navigable by naval units passing through. Third, if found on a cliff the city should show the graphic suggesting that land units can indeed embark/disembark there. No gameplay changes were made in this mod.