Store list of files that are part of the project

Store a list of all files that are referenced when resolving the
project as part of the project.

This list is then processed to check whether the project needs to be
re-resolved.

Change-Id: Iccb8928a5349546c22a9615256a505bebf5de567
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>