Remember previously opened folders

[jtpio]

For now we need to re-open the folders manually after reloading the page.

Maybe the previous folder should be automatically opened is possible (best effort). That could be convenient for those always working with the same folder.

This could also be made opt-in or opt-out via the settings.

[martinRenou]

Maybe we can change the behavior introduced in this commit, and instead of .cd('/') do a .cd( to the stored directory.

Ideally we would store the state on a per-root basis.