Add shallow water to oasis like ford terrain

Resolves  #8753

data/core/terrain.cfg

@@ -354,11 +354,11 @@ Most units receive 20 to 40% defense in sand."
     default_base=Dd
     string=^Do
     # Note: we must do the aliasing this way to allow the terrain to show up in the "Sand" terrain help group
-    aliasof=Dt
-    def_alias=_bas
-    mvt_alias=_bas
+    aliasof=Dt, Wst
+    def_alias=_bas, Wst
+    mvt_alias=_bas, Wst
     heals=8
-    editor_group=desert
+    editor_group=desert, water
     help_topic_text= _ "A welcome sight to any traveler, an oasis allows units to heal as if stationed in a village, but provides no income or defensive advantage."
 [/terrain_type]