AddLibraryWizard: wrap text on snippets label

In this way dialog doesn't grow in width when the label contains long
lines.

Change-Id: Ibd5906912c18c8e4b27959ff5a7aeda258d6995a
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>