Include a "Locations" list to the left side of the pqFileDialog. It is updated every time the dialog is created with "special" directories, which includes drives. This resolves an issue on Windows, because while the "Favorites" list includes drives by default, the favorites list is saved in the settings and not updated once created, so new drives like USB keys or newly mapped network drives don't appear. Users can also remove drives from the favorites list, and now they will still appear in the Locations list.
Add a "Media" special directory on Linux, pointing to common mount directories for removable drives.