Add D-Bus API

Fix activation of radio menu items (#24)

Add basic settings

Fix modal window behavior on X11

Expand search entry in header bar

Make popup window modal

Add padding to list columns

Improve README heading

Update copyright year

Support programs that do not use Gtk.Application

Adjust spacing in header bar

Wait for theme's style context to become available

Try to get button label from enclosing toolbar button widget, if present

Extract commands from MenuButton popup menu if present

Guard against button.get_name() returning null