Sqlite: Add foreign key support

It is still only support references in columns but so far it is enough.

Change-Id: Iebb4866cf738d651270e54357b5e4a2837f05417
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>

src/libs/sqlite/sqliteexception.h

@@ -272,4 +272,12 @@ public:
     {}
 };
 
+class ForeignKeyColumnIsNotUnique : public Exception
+{
+public:
+    ForeignKeyColumnIsNotUnique(const char *whatErrorHasHappen)
+        : Exception(whatErrorHasHappen)
+    {}
+};
+
 } // namespace Sqlite