Update to 1.15

Most of the port is pretty simple. The main problems are regarding
changes to Minecraft's rendering system.

 - Remove several rendering tweaks until Forge's compatibility it
   brought up-to-date
    - Map rendering for pocket computers and printouts
    - Item frame rendering for printouts
    - Custom block outlines for monitors and cables/wired modems
    - Custom breaking progress for cables/wired modems

 - Turtle "Dinnerbone" rendering is currently broken, as normals are not
   correctly transformed.

 - Rewrite FixedWidthFontRenderer to to the buffer in a single sweep.
   In order to do this, the term_font now also bundles a "background"
   section, which is just a blank region of the screen.

 - Render monitors using a VBO instead of a call list. I haven't
   compared performance yet, but it manages to render a 6x5 array of
   _static_ monitors at almost 60fps, which seems pretty reasonable.

src/main/java/dan200/computercraft/shared/Config.java

@@ -324,7 +324,7 @@ public final class Config
     }
 
     @SubscribeEvent
-    public static void sync( ModConfig.ConfigReloading event )
+    public static void sync( ModConfig.Reloading event )
     {
         // Ensure file configs are reloaded. Forge should probably do this, so worth checking in the future.
         CommentedConfig config = event.getConfig().getConfigData();