Edited Issue: [RTM] Serialized SSDL contains auto generated namespace prefix for store extensions [1499]

When generating a model from the database the designer adds some attributes in the "http://schemas.microsoft.com/ado/2007/12/edm/EntityStoreSchemaGenerator" previously we would define the namespace on the Schema element (root element for SSDL) and give it the "store" prefix. Now we no longer treat it in a special way and therefore the XmlWriter defines the namespace as needed and creates a potentially random prefix.

Expected:
Namespace defined on the Schema element as: ```xmlns:store="http://schemas.microsoft.com/ado/2007/12/edm/EntityStoreSchemaGenerator"```
and
```
<EntityContainer Name="ParentChildModelStoreContainer">
<EntitySet Name="ChildEntities" EntityType="Self.ChildEntities" Schema="dbo" store:Type="Tables" />
<EntitySet Name="ParentEntities" EntityType="Self.ParentEntities" Schema="dbo" store:Type="Tables" />
<AssociationSet Name="FK_ParentEntityChildEntity" Association="Self.FK_ParentEntityChildEntity">
```

Actual:

```
<EntityContainer Name="ParentChildModelStoreContainer">
<EntitySet Name="ChildEntities" EntityType="Self.ChildEntities" Schema="dbo" p3:Type="Tables" xmlns:p3="http://schemas.microsoft.com/ado/2007/12/edm/EntityStoreSchemaGenerator" />
<EntitySet Name="ParentEntities" EntityType="Self.ParentEntities" Schema="dbo" p3:Type="Tables" xmlns:p3="http://schemas.microsoft.com/ado/2007/12/edm/EntityStoreSchemaGenerator" />
<AssociationSet Name="FK_ParentEntityChildEntity" Association="Self.FK_ParentEntityChildEntity">
```

Note that the fix is probably in runtime since we now use runtime to write the model.