Webclient: fix view config overriding (#208).

This change introduced 2 days ago is now reverted:

> NOTE 2: an **association definition** can no longer override a child type's view configuration setting
> with a **falsish** value (0, "", false). This is regarded as not needed anymore because the semantics
> of the former "Viewable" and "Editable" settings is inverted (see last commit).

Now the view config overriding bahavoir is exactly like before: you **can** override with falsish values.

Thanks, dgf for reporting!

See ticket 208.