Automatically create correct sized layer when adding subpresentation

When user adds a sub presentation to layer, it is scaled to same size as the target presentation is. This is not a problem if the presentations are in same size. If not, presentation is scaled to match the layer size, being stretched and covering whole area.

Target layer should be automatically scaled to match the subpresentation size and by default it should be centered. This should be fixes asap.

Future: adjust layer size and position using modifiers