more detailed wetland presets (closes #281)

add presets for all categories currently documented at https://wiki.openstreetmap.org/wiki/Key:wetland

also drop the tidal/salt fields where they do not apply to the more specific wetland presets

data/fields/wetland.json

@@ -1,5 +1,19 @@
 {
     "key": "wetland",
     "type": "combo",
-    "label": "Type"
+    "label": "Type",
+    "strings": {
+        "options": {
+            "marsh": "Marsh",
+            "reedbed": "Reed Bed",
+            "saltmarsh": "Coastal Salt Marsh",
+            "tidalflat": "Tidal Flat",
+            "wet_meadow": "Wet Meadow",
+            "swamp": "Swamp",
+            "mangrove": "Mangrove",
+            "bog": "Bog",
+            "fen": "Fen",
+            "string_bog": "String Bog"
+        }
+    }
 }