move world-related functions from core library

res/layouts/pages/new_world.xml.lua

@@ -21,7 +21,7 @@ function create_world()
     local seed = document.seed_box.text
     local generator = settings.generator
     session.reset_entry('new_world')
-    core.new_world(name, seed, generator)
+    app.new_world(name, seed, generator)
 end
 
 function world_name_placeholder()

res/layouts/pages/pause.xml

@@ -2,7 +2,7 @@
     <button onclick='menu:reset()'>@Continue</button>
     <button onclick='menu.page="content?mode=world"'>@Content</button>
     <button onclick='menu.page="settings"'>@Settings</button>
-    <button onclick='core.close_world(true)'>
+    <button onclick='app.close_world(true)'>
         @Save and Quit to Menu
     </button>
 </panel>

res/layouts/templates/world.xml

@@ -2,7 +2,7 @@
     size='380,66'
     color='#0F1E2DB2'
     hover-color='#162B3399'
-    onclick='core.open_world("%{name}")'
+    onclick='app.open_world("%{name}")'
 >
     <image pos='1' src='%{icon}' size='96,64'></image>
     <label pos='104,8'>%{name}</label>
@@ -11,7 +11,7 @@
             color='#00000000'
             hover-color='#FFFFFF2B'
             padding='0'
-            onclick='core.delete_world("%{name}")'>
+            onclick='app.delete_world("%{name}")'>
         <image src='gui/delete_icon' size='32,32' color='#FFFFFF50'/>
     </button>
     <label color='%{versionColor}' pos='317,44'>%{versionString}</label>