Fix issues highlighted

Signed-off-by: Bimal Yashodha <kb.yashodha@gmail.com>
Make callbacks non mandatory

Signed-off-by: Bimal Yashodha <kb.yashodha@gmail.com>
Escape HTML

Signed-off-by: Bimal Yashodha <kb.yashodha@gmail.com>
Check whether the db is not system schema

Signed-off-by: Bimal Yashodha <kb.yashodha@gmail.com>