Add a soft reload that reloads scene files.

`Reload` currently attempts to reload the world. This fails if the current selected world is not the same as the world in the scene. It is also wasteful if you reload just to switch Octree implementations for example.

There should be a "soft reload" that reloads the scene files. One use case, for example, might be to load a world using the DISK octree, then switch to DICT, and then soft reload. This should reload the octree from the `.octree2` file.

Start by locating the existing Reload action and the scene-loading path in the Java application. Trace how the selected world, scene files, and `.octree2` data are handled; done means a soft reload refreshes scene files and can reload the octree after changing its implementation without reloading the world.

Written by the indexing model from the issue text.