Add credential helper settings in Settings Dialog

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Add simplified credential helper selection

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Commit the changes after code review

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Fixed issue #522: Store password for HTTP

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>