Implement marine unit visibility and movement logic; add map loading from JSON

conf/keybinding_paused.json

@@ -0,0 +1,6 @@
+{
+    
+    "reset_game": ["Return", 13],
+    "pause": ["P", 16],
+    "quit": ["Q", 12]
+}

conf/keybinding_start_menu.json

@@ -0,0 +1,6 @@
+{
+    
+    "start_game": ["Return", 13],
+    "toggle_full_screen": ["F"],
+    "quit": ["Q", 12]
+}

conf/keymap_game.json

@@ -0,0 +1,7 @@
+{
+
+    "keydown:up": "scroll_up",
+    "keydown:down": "scroll_down",
+    "keydown:left": "scroll_left",
+    "keydown:right": "scroll_right"
+}