Add bookmarks expander under the tabbed pane

Mark whenever a fallback font is used for a glyph

Mark reserved, non-printable, and unassigned characters

Add handheld-layout (with compile-time opt-in as default):
	alternative 1: put group list, as combo box, above table
	alternative 2: put group list as tab
	also: skip the menubar (but add the accelerators)

Remember some settings

Add font blacklist

Add support for command line operands: select listed fonts by path

Add editor to font drop-down to make it easier to select a font

Scrolling inside a GtkScrolledWindow or LogicalScrollPane shall steal focus

Scrolling with Control held down shall change zoom. The hovered cell shall
remain visible, preferably at the same Y position as the pointer. The pointer
shall jump to the new position of the cell so account for it being impossible
to ensure that cell remains at the same X position as the pointer.