Improve UAT on layout

* Move cucumber features regarding the layout protocol in
  layout/protocol;
* Add new cucumber features to test uh-layout integration in uh-wm, at
  least simple mapping and focus behavior;
* Add new acceptance testing helpers

lib/uh/wm/testing/acceptance_helpers.rb

@@ -60,6 +60,10 @@ module Uh
           @x_client ||= XClient.new
         end
 
+        def x_focused_window_id
+          Integer(`xdpyinfo`[/^focus:\s+window\s+(0x\h+)/, 1])
+        end
+
         def x_key key
           fail "cannot simulate X key `#{key}'" unless system "xdotool key #{key}"
         end
@@ -73,6 +77,10 @@ module Uh
           end.any?
         end
 
+        def x_window_id
+          @x_client.window_id
+        end
+
         def x_window_name
           @x_client.window_name
         end
@@ -81,6 +89,10 @@ module Uh
           x_client.map.sync
         end
 
+        def x_window_map_state
+          `xwininfo -id #{x_window_id}`[/Map State: (\w+)/, 1]
+        end
+
         def x_clients_ensure_stop
           @x_client and @x_client.terminate
         end
@@ -135,6 +147,10 @@ module Uh
             end
           end
 
+          def window_id
+            @window.id
+          end
+
           def window_name
             @name
           end