Reconsider placement and semantics of OnDelete element

Currently the OnDelete element is on the dependent side and specifies "what happens here if over there the last thing goes away", i.e. an observer/event subscription pattern. This may have been inspired by SQL's ON DELETE, which is also specified on the dependent side.

The "original" OnDelete element of OData V2/V3 seems to be specified on the principal side of the association, unfortunately not explicitly stated, only deducible from the only given example:

<Association Name="CProductCategory">
<End Type="Self.CProduct" Multiplicity="*" />
<End Type="Self.CCategory" Multiplicity="0..1">
<OnDelete Action="Cascade" />
</End>
</Association>

If the category goes away, it notifies its products to also go away.