Edited Feature: Add foreign key information to the associations in the $metadata document [1094]

When there is an entity in a model that has an entity that explicitly exposes the foreign key of an association to another entity, make that information visible and available in the $metadata document.

For example:

```
<EntityType Name="Customer">
<Key>
<PropertyRef Name="Id"/>
</Key>
<Property xmlns:p6="http://schemas.microsoft.com/ado/2009/02/edm/annotation" Name="Id" Type="Edm.Int32" Nullable="false" p6:StoreGeneratedPattern="Identity"/>
<Property Name="Name" Type="Edm.String" MaxLength="Max" FixedLength="false" Unicode="true"/>
<NavigationProperty Name="Orders" Relationship="WcfDataServicesForeignKey.Customer_Orders" ToRole="Customer_Orders_Target" FromRole="Customer_Orders_Source"/>
</EntityType>
<EntityType Name="Order">
<Key>
<PropertyRef Name="Id"/>
</Key>
<Property xmlns:p6="http://schemas.microsoft.com/ado/2009/02/edm/annotation" Name="Id" Type="Edm.Int32" Nullable="false" p6:StoreGeneratedPattern="Identity"/>
<Property Name="CustomerId" Type="Edm.Int32" Nullable="false"/>
<Property Name="Purchased" Type="Edm.DateTime" Nullable="false"/>
<Property Name="Total" Type="Edm.Double" Nullable="false"/>
</EntityType>
<Association Name="Customer_Orders">
<End Type="WcfDataServicesForeignKey.Customer" Role="Customer_Orders_Source" Multiplicity="1">
<OnDelete Action="Cascade"/>
</End>
<End Type="WcfDataServicesForeignKey.Order" Role="Customer_Orders_Target" Multiplicity="*"/>
<ReferentialConstraint>
<Principal Role="Customer_Orders_Source">
<PropertyRef Name="Id"/>
</Principal>
<Dependent Role="Customer_Orders_Target">
<PropertyRef Name="CustomerId"/>
</Dependent>
</ReferentialConstraint>
</Association>
```

This is the behavior WCF Data Services implement, and it's required for third party OData client libraries like breeze.js to work against Web API OData properly.