Improve prelude-open-with

Now it uses `xdg-open` where it makes sense. It also accepts a prefix
argument that forces manual selection of a command to run.
Don't try to save files when you don't have the permissions to do so
Quote buffer-file-name in prelude-open
Simplify prelude-rename-file-and-buffer
removed the non-working fullscreen code
updated ELPA packages
Merge remote-tracking branch 'prelude/master'
removed redundant statements