Computed offsets to parent platform in mount wizard

Display computed offsets to the root if parent platform is selected.

Computed offsets should be displayed in the following places:

• MountWizard Step 4 (Add mount information)
• MountWizard Step 5 (Submit)
• Mount Information when selecting a node in the configuration tree

The relative offset is displayed in all these places. The calculated offset to the root could be displayed next to it for example.

nice to have from #268 (closed)