XD map loading on Dev should be optional

[marianopeck]

As discussing internally, if apps only define packaging rules through the hooks mentioned here then loading apps on the dev wouldn't be necessary and loading on runtime should be enough.

But...if you have apps that implement app level #packagingRulesFor: with complex rules, then apps need to be loaded on the dev.

For the moment, we always load the XD map on the dev, but in the future it would be nice to make this optional for projects that don't need it (like Seaside Traffic Light)