projects: mark output files as outdated

[malmeloo]

It would be useful if output files would automatically be marked as outdated / stale if the input files change. They should then be marked as "up-to-date" again once they have been updated by the synthesis / PnR tool. This allows users to easily see whether their output files are still fresh.

This could perhaps be visualized by "graying out" the file name in the output file tree.