Fix setting for multiple action keywords

1. completed rewrite the action keyword setting logic.
2. Fix setting for multiple action keywords in #352
3. Fix setting for Web Search plugin

Wox.Plugin/PluginPair.cs

@@ -15,5 +15,24 @@
         {
             return Metadata.Name;
         }
+
+        public override bool Equals(object obj)
+        {
+            PluginPair r = obj as PluginPair;
+            if (r != null)
+            {
+                return string.Equals(r.Metadata.ID, Metadata.ID);
+            }
+            else
+            {
+                return false;
+            }
+        }
+
+        public override int GetHashCode()
+        {
+            var hashcode = Metadata.ID?.GetHashCode() ?? 0;
+            return hashcode;
+        }
     }
 }