Allow saving non-existent file

Hello!

$ ls foo.txt
ls: cannot access 'foo.txt': No such file or directory
$ mousepad foo.txt

Mousepad disables "Save" action for non-existent blank file. After pressing Ctrl-S or clicking "Save" should save the non-existent file creating the file in doing so. gedit does this.

Also, For non-existent file the window title and tab title should reflect the fact that the contents are not saved on the disk. i.e. file is not on disk by appending * to window title and changing color of tab title to red.