Refactor thread responses into an enum.

Lays ground work for different types of views, i.e. email, news, docs, etc.

web/graphql/show_thread.graphql

@@ -1,47 +1,49 @@
 query ShowThreadQuery($threadId: String!) {
   thread(threadId: $threadId) {
-    threadId,
-    subject
-    messages {
-      id
+    __typename ... on EmailThread{
+      threadId,
       subject
-      tags
-      from {
-        name
-        addr
-      }
-      to {
-        name
-        addr
-      }
-      cc {
-        name
-        addr
-      }
-      timestamp
-      body {
-        __typename
-        ... on UnhandledContentType {
-          contents
-          contentTree
-        }
-        ... on PlainText {
-          contents
-          contentTree
-        }
-        ... on Html {
-          contents
-          contentTree
-        }
-      }
-      path
-      attachments {
+      messages {
         id
-        idx
-        filename
-        contentType
-        contentId
-        size
+        subject
+        tags
+        from {
+          name
+          addr
+        }
+        to {
+          name
+          addr
+        }
+        cc {
+          name
+          addr
+        }
+        timestamp
+        body {
+          __typename
+          ... on UnhandledContentType {
+            contents
+            contentTree
+          }
+          ... on PlainText {
+            contents
+            contentTree
+          }
+          ... on Html {
+            contents
+            contentTree
+          }
+        }
+        path
+        attachments {
+          id
+          idx
+          filename
+          contentType
+          contentId
+          size
+        }
       }
     }
   }