Fixed|Client: Comment in appconfig.de module
UI|Client|DialogWidget: Buttonless dialogs

Normally space is reserved for a row of buttons in the bottom of a
dialog. With the Buttonless flag, the buttons menu is left out from
the dialog.
Updater|Config|Client: Updater's default config moved to appconfig.de

Previously this was handled by native code in UpdaterSettings, but
now Doomsday Script has all the information available to make the
proper decisions about the Updater's default settings.

Having this in appconfig.de ensures that the normal de::Config
(re)configuration mechanism can be applied to the updater as well.
libgui|PersistentCanvasWindow: Added audience for attribute changes
libdeng2|OperatorRule: Added a static 3-way maximum method
UI|Client: Basic implementation of video settings

The Video Settings dialog allows changing the display mode and window
attributes. The "Toggle Fullscreen" and "Show FPS" options were
relocated into the new dialog.

Improved ChoiceWidget with configurable opening direction and added
the "togglecentered" console command.