toolbar: Improve path bar actions discoverability

For 3.30 Nautilus implemented a new path bar design that provided a the view background menu in the path bar labels that was usually unavailable in list view.

While this is a good step forward, the discoverability of the path bar buttons was not good, users didn't figure out those are actual buttons and they can click in them.

This work tries to fix that by buttinizing again the path bar, while matching better with the new gtk stylesheet.

Changes are the style of the path bar buttons and adding a "New Folder" to the hamburguer menu.

Fixes: #734 (closed)