Add support for including within specific configurations

Add support for including within specific configurations

The current support for includes are limited to including a view
within the "base" layouts (defined in layouts/). This changeset
generalizes this to track ALL include-sources (such as an include from
the landscape version) and offers to let you view and edit the current
view within each of those specific configurations.  The configuration
will be switched to one that is compatible with the outer, including
view.  It is possible that this will switch to a different inner view;
that seems better than trying to force editing an inner view in an
outer view that won't actually be shown at runtime.

We should enhance the configuration chooser such that it will only
offer options in its various combo boxes that are compatible with the
inner view as well. That is not addressed by this changeset.

Change-Id: Id5171d367cf65e2403bbac1640a179de4b420bd6