Add two new levels

dist/assets/levels/6.txt

@@ -0,0 +1,7 @@
+[/~   ] [-] [- ] [ -          ] [-;t|D   ]
+[|    ]
+[|    ] [x] [/~] [ -          ] [~\      ]
+[|;d|B] [x] [| ] [ |-;t|C;A;;d] [-|;d|A  ]
+[|    ] [x] [\_] [-^-;s;D;2   ] [-|;;B;;d]
+[|    ] [x] [x ] [x           ] [ |      ]
+[|;;C ] [x] [x ] [x           ] [ \_     ] [-;f]

dist/assets/levels/7.txt

@@ -0,0 +1,9 @@
+[|-;f  ] [-;;B;;d] [x] [x     ] [x      ] [-;;D] [-]
+[|     ]
+[|;t|D ] [ |;;C  ]
+[|     ] [ |     ] [x] [- ;t|G] [-;;F;;d] [-;;A;2] [-;;E;2] [-   ] [-] [-;t|C]
+[|     ] [ |;d|F ]
+[|     ] [ |     ]
+[|     ] [ |;t|E ] [x] [| ;t|B]
+[|-    ] [_/;t|A ] [x] [\_    ] [-      ] [-;d|B ] [-;;G]
+[|;s   ]

dist/assets/levels/_list.txt

@@ -4,3 +4,5 @@ level_file;field_lifetime;level_code;message
 3.txt;1;FENCES;Dangerous red tiles can be deactivated.
 4.txt;1;DURABILITY;You can step more than once on yellow tiles.
 5.txt;1;TELEPORT;Violet tiles teleport you... somewhere.
+6.txt;1;DETACHED;This one should be easy.
+7.txt;1;CHALLENGE;For the first time, something challenging.