Inform the user when saving an image

[douglascdev]

The current saving function writes to the console to say the image was saved. It should show a dialog with text saying whether it saved successfully(and the path, if so) or if there was an error, say so and log the exception.

Instead of a dialog, it would make more sense to do it like vim and show the message in #15's input after writing :w, so this issue now depends on #15 being completed.

[douglascdev]

@Bleit51 I saw you forked the repo just before I edited this issue, were you going to try solving this one? Sorry If that was the case. And if so, please wait until #15 is done and merged.