QmlDesigner.ItemLibrary: Use ScrollView instead of custom solution

With ScrollView the mouse wheel does work.

Task-number: QTCREATORBUG-10708
Change-Id: I6f9a85421049f1d2e56608340533af5b28d5c7ab
Reviewed-by: Thomas Hartmann <Thomas.Hartmann@digia.com>
Doc: CodePaster is no longer integrated in Qt Creator

Remove information about CodePaster. Remove info on other obsolete
settings, and explain all current settings and options.

Change-Id: Ib128ec733808b12a79ec0e835ecbc0bfb889ab2b
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>