add 'healthcare' as main tag

Given that the tag is most of the time duplicated by an amenity
tag which is already imported, only import it as a fallback when
there is no name.

Fixes #2609.

settings/import-extratags.style

@@ -180,7 +180,7 @@
     }
 },
 {
-    "keys" : ["junction"],
+    "keys" : ["junction", "healthcare"],
     "values" : {
         "" : "main,fallback,with_name"
     }

settings/import-full.style

@@ -180,7 +180,7 @@
     }
 },
 {
-    "keys" : ["junction"],
+    "keys" : ["junction", "healthcare"],
     "values" : {
         "" : "main,fallback,with_name"
     }