Minimap, hotkeys and lot of other changes

* Begin working on a new layout system for UIMinimap and later UIMap,
this new layout system allows to add widgets to the minimap
* Add option to disable motd
* Rework hotkey binding
* Lots of fixes in hotkeys manager
* Add fullmap view using Ctrl+Shift+M
* Prevent some crashs in ThingType draw
* Add function to load minimap from PNG files
* Fixes in minimap saving
* Fixes in Tile::isClickable
* Add UIMapAnchorLayout, new layout for maps
* Fix freezes in win32 when pressing alt key

modules/corelib/ui/uiscrollbar.lua

@@ -224,7 +224,9 @@ end
 
 function UIScrollBar:setText(text)
   local valueLabel = self:getChildById('valueLabel')
-  valueLabel:setText(text)
+  if valueLabel then
+    valueLabel:setText(text)
+  end
 end
 
 function UIScrollBar:onGeometryChange()