Revert "Remove database-related message content usage"

This reverts commit 0b211db023.

sql/structure.sql

@@ -28,6 +28,21 @@ CREATE TABLE
     private_help_channel_id TEXT
   );
 
+CREATE TABLE
+  IF NOT EXISTS messages (
+    id TEXT PRIMARY KEY ON CONFLICT REPLACE,
+    author_id TEXT NOT NULL,
+    author_name TEXT NOT NULL,
+    channel_id TEXT NOT NULL,
+    attachments TEXT NOT NULL,
+    stickers TEXT NOT NULL,
+    content TEXT NOT NULL
+  );
+
+CREATE INDEX IF NOT EXISTS index_authors ON messages (author_id);
+
+CREATE INDEX IF NOT EXISTS index_channels ON messages (channel_id);
+
 CREATE TABLE
   IF NOT EXISTS tickets (id INTEGER PRIMARY KEY, message_id TEXT NOT NULL);