Add credential helper settings in Settings Dialog

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Signed-off-by: Sven Strickroth <email@cs-ware.de>
Add simplified credential helper selection

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Signed-off-by: Sven Strickroth <email@cs-ware.de>
Fixed issue #522: Store password for HTTP

Signed-off-by: Sup Yut Sum <ch3cooli@gmail.com>
Merge branch 'issue-522'
Dropped superfluous space

Signed-off-by: Sven Strickroth <email@cs-ware.de>