Fix broken list requests in CodePaster.

Pastebin.com-support: Remove header from list data.
KDE Paste: Add trailing slash to prevent redirection.

Task-number: QTCREATORBUG-9547
Change-Id: If47c4bc64767efb6f1a17db22ff9e0dbee3841bc
Reviewed-by: Michael Bruning <michael.bruning@digia.com>
Reviewed-by: Robert Loehning <robert.loehning@digia.com>
Reviewed-by: Eike Ziller <eike.ziller@digia.com>