Sqlite: Cleanup table and column handling

Using values instead of pointers makes the handling much easier. We can
remove ColumnDefinition too, and use SqliteColumn instead.

Change-Id: I224db9cc569c4dfb6e2746179b02096904bfbccb
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

tests/unit/unittest/sqlitedatabase-test.cpp

@@ -81,9 +81,7 @@ TEST_F(SqliteDatabase, CloseDatabase)
 
 TEST_F(SqliteDatabase, AddTable)
 {
-    SqliteTable *sqliteTable = new SqliteTable;
-
-    database.addTable(sqliteTable);
+    auto sqliteTable = database.addTable();
 
     ASSERT_THAT(database.tables(), Contains(sqliteTable));
 }