[improvement] show all files from all storage

[fallsdevil]

Hello, I've been using this app for a while, but I realized that it's not like other file managers. For example, when you click on "documents" in the side panel, the files shown are always limited to internal storage, I use an SD card and I'd like it to show the files on the SD card too, equally with the other tabs "videos", "images", etc.