libappfw|GuiWidget: Enabling/disabling widget state serialization
UI|Client: GamesDialog can be opened in different modes

Having everything in the same dialog is too confusing for UX,
even though the implementation benefits from it. Now the singleplayer
and multiplayer games are accessed separately, using different
modes.
UI|Task Bar: Updated DE menu with game selection items
UI|Multiplayer: "Join Game" main menu item opens a GamesDialog

The old multiplayer UI has been bypassed.
Cleanup|Client: Removed old Control Panel / network setup UI sources

These are now fully obsolete.
Cleanup|Client: Removed large portion of old GUI code

The remaining parts are the system fonts and some basic drawing
functions used by the Bias Light editor and some debug visuals.
Fixed: Build failure
Merge branch 'ui-multiplayer'
Documentation|libgui: Clarified Atlas API docs
libappfw|DialogWidget: Place image-only buttons to the left