WIP eeschema: Add option for renaming sheets in the Hierarchy tree view

This MR adds a right click context menu to the Hierarchy tree view in eeschema:

After selecting the rename action the active treeview item became editable (without the page: x suffix):

I think this renaming method is more intuitive than the editing of the hierarchical sheet names in the root page.

The context menu in the hierarchical tree adds some other possibilities (like deleting the hierarchial sheets) as well.