remove superfluous explicitlyDependsOn

Change-Id: I5f032264a9497f564caeec24a0a389c1cbe593d8
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>
remove dumpProductBuildConfig

This function is dead since quite a while and its value for debugging is
very low.

Change-Id: I99c52c8729c5f649b7200beca92a70e00c32a323
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>
move file dependencies to dedicated class

File dependencies are a very simple variant of artifact.
We save space and structure the code more clearly by introducing the
FileDependency class.

Change-Id: I36b95794f9d6d3d739ea4836ebc831848a89de98
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>