Render water areas differently when tagged salt=yes

[jeisenbe]

Expected behavior

• The tag salt=yes should be used to render salt lakes differently than fresh water lakes
• Currently the tag is used over 14,000 times, including 8000 uses with natural=water: https://wiki.openstreetmap.org/wiki/Key:salt
• It was approved in 2011: https://wiki.openstreetmap.org/wiki/Proposed_features/Water_details

Actual behavior

• Oceans, seas, lagoons and salt lakes are currently all rendered the same as freshwater rivers.
• Recently we just began to render wetland=saltmarsh differently than wetland=marsh by using a random white dot pattern.

[jeisenbe]

Usage trend from taghistory:

[jeisenbe]

Also related to rendering landuse=salt_pond - see #545