Improve the file explorer

caoimhebyrne

At the moment, the file explorer is quite limited, and is missing a lot of basic functionality, like: - Creating folders - File/folder context menus - Creating new files - Creating a sub-folder - Deleting a file - Renaming a file - etc.

caoimhebyrne

As a note, this was originally meant to be completed in #2, but the PR quickly became stale and we should have a more expressive way to handle file actions.