glib: Aggregate individuals widgets as one single show_all
glib: Move add annotation type to main widget

Prepare the way to add an annotation by interacting directly with
the drawing area instead of entering the coordinates by hand. The
first step is move the interaction to the main annotation widget.
glib: Add annotations interactively

Prepare the render area to add annotations interactively instead
of button/dialog.
glib: Remove button to add annotations with a dialog

Instead, the annotation will be added interactively in the render
area.