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/table.lua

@@ -13,6 +13,12 @@ function table.dump(t, depth)
   end
 end
 
+function table.clear(t)
+  for k,v in pairs(t) do
+    t[k] = nil
+  end
+end
+
 function table.copy(t)
   local res = {}
   for k,v in pairs(t) do