Display error message when adding an existing configuration.

Change-Id: I44ce937ab9bab65c3680c11304e1ba5a6c366e1e
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@digia.com>
Show error message when project cannot be opened.

Change-Id: I72c701c0a6d4a40f17998d46e21e9dc117cf064e
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@digia.com>