glib-demo: Extend demo for FreeText annotations

Adds font color, font size, intent properties of freetext annotations.
Also allows adding new free text annotations.
glib: Add PopplerAnnotBorder boxed type

This type is used to wrap the AnnotBorder class in the core to represent
border of annotations.
glib: Add border to annotations
glib-demo: Add border to free text annots
glib-demo: FIXUP for freetext