Open dialog for browsing using Padre::File

[Sewi]

Padre::File should enable Padre to handle remote files the same way as local files.

We need an open-dialog which requests a URL from the user or uses one from a projects padre.xml and then uses Padre::File to scan directories and show files.

Padre::File doesn't really need a protocol://host/path/file syntax, please consider the same for the dialog (a Plugin could enable URLs like nfs.server.com:/path/file or smb_server/share/file)