UI|Client: Added a tutorial dialog

Todo: Widget for binding the console key.
libappfw|Added: Special button with a small auxiliary button inside

AuxButtonWidget has an auxiliary button inside that can be used for
extra functionality.
Fixed|libappfw|LabelWidget: Updating label's margins
libdeng2: Added more character symbols (Alt)
libappfw|libgui: Key modifier related cleanup
UI|Bindings: Added widget for making an input binding

The bindings subsystem was enhanced with functions for finding
existing bindings for a command and deleting bindings based on
the bound command.

InputBindingWidget currently supports only command bindings for
the keyboard device.
Tutorial: Added console key binding widget

The tutorial now offers an opportunity to change the console shortcut
key. This is only shown when a game is loaded, because in Ring Zero
bindings are currently not persistent.
UI|Console: Added menu item for setting console shortcut key
libdeng2|FS: Print contents of InputError exception
libdeng2|FS: Use a dev warning for InputError contents
libappfw|GuiRootWidget: Added method for finding GuiWidgets
Tutorial|Client: Added a glow to highlight UI elements

Draw attention to the correct place.
UI|Client: Minor tweaks

Don't allow starting tutorial in busy mode.
Savegame Tool: Savegames for Hexen in the old ver3 format not supported

The result of a serialization mishap, the side data in the map segment
is strewn with junk values, meaning that straight conversion of such
savegames is not presently possible.
Merge remote-tracking branch 'remotes/origin/master' into savegame-refactor
Fixed|Bindings|UI|Client: Compiler warning (unsafe mix of bool / ddboolean_t)
Fixed|libcommon: Fully reinitialize the game SaveSlots when changing game

The game plugin might not be unloaded when the game is changed, so we
need to fully reinitialize the save slots each time.