[FR] Add Work in ... feature to context menus

[carstenbauer]

As discussed with @pfitzseb on Slack, it would make sense to provide access to the Work in ... features (setting the working directory of the active Julia session) in context menus in the project tree view.

Eventually one should be able to right-click on a file or a project in the tree view on the left and have an entry like "Set as current working directory" (or similar).