Defined a function to create a note interactively

Currently the easiest way to implement note creation that I can think of
is simply two blocking prompts for the note title and content. Not very
flexible, but it works so that is the functionality that will exist
initially until it can be enhanced later through polish.
Added create-button callback to create notes

The callback uses the previously defined create-note-interactive
function to prompt for the new note to insert. Once the note is created,
the title-listbox is refreshed. Since the title-listbox refreshing is
done in multiple locations, it is probably better to define a function
that handles the refreshing of the title-listbox's content.