Inspector could have a menu on top

[slhh]

The inspector could have a menu on top.

• This would be a natural position for the controls of Inspector: Delete all fields and tags #2979 and Option to make invisible relations visible #2980
• Moving the delete operation from the radial menu to this menu might be useful, especially in view of Edit menu operations are not available for invisible relations #2977
• Moving some other operations from the radial menu to this menu could free space in the radial menu in case this is required in future.
• The control to go back to the multiselect list according to Multiselect list: Store multiselection when opening the inspector by clicking an item #2964 could be placed in this menu.

[jfirebaugh]

This may well be where #1994 ends up. But I don't think we need a separate issue.