Create an Options menu with a way to move notebooks

[ccordoba12]

So people could use an untitled notebook to do some exploratory work and then they'd like to rename and move that notebook to another place.

We need to add an option in the Options menu of the notebook to do exactly that :-)

@dalthviz, please work on this one too.

[ccordoba12]

Some ideas for this:

1. The option must be called Save as....
2. As with the Editor, it must open a file dialog to pick up a file name and location in the operating system.
3. After the user has selected that, we must close the current untitled file, move that file to the user's selected path and reopen it with create_new_client again.

Note: Unfortunately, that won't preserve the kernel of the untitled notebook with the new file, but I think that's ok for a 0.1 version.