web: add basic graphql view thread, no body support.

web/graphql/show_thread.graphql

@@ -0,0 +1,21 @@
+query ShowThreadQuery($threadId: String!) {
+  thread(threadId: $threadId) {
+    subject
+    messages {
+      subject
+      from {
+        name
+        addr
+      }
+      to {
+        name
+        addr
+      }
+      cc {
+        name
+        addr
+      }
+      timestamp
+    }
+  }
+}