Change ID fields in SQL to be unique

src/sqlite/chat_index.sql

@@ -1,6 +1,6 @@
 -- chat index table
 CREATE TABLE IF NOT EXISTS chat_index (
-    id TEXT NOT NULL,
+    id TEXT NOT NULL UNIQUE,
     is_group_chat BOOLEAN DEFAULT 0 NOT NULL CHECK (is_group_chat IN (0, 1)),
     title TEXT NOT NULL,
     description TEXT,

src/sqlite/msgdata_template.sql

@@ -1,7 +1,7 @@
 -- msgdata_template definition
 -- TODO Add IF NOT EXISTS to prevent panics
 CREATE TABLE msgdata_{chat_id} (
-	msg_id TEXT NOT NULL,
+	msg_id TEXT NOT NULL UNIQUE,
 	timestamp INTEGER NOT NULL,
 	sender_id TEXT NOT NULL,
 	msg_type INTEGER NOT NULL,

src/sqlite/users.sql

@@ -2,7 +2,7 @@
 
 CREATE TABLE IF NOT EXISTS users (
 	id TEXT NOT NULL PRIMARY KEY,
-	user_name TEXT NOT NULL,
+	user_name TEXT NOT NULL UNIQUE,
 	display_name TEXT,
 	activated BOOLEAN DEFAULT 0 NOT NULL CHECK (activated IN (0, 1)),
 	created INTEGER NOT NULL,