Open Prompt for new scenes

[jackjt8]

Following all the issues surrounding Y min/max clip and Min/Max Y level and, considering potential solutions, I believe that opening a New Scene prompt/window may help alleviate issues.

Upon using New scene from selection OR Load selected chunks (only for first usage) we should open a New Scene window to ask the user for the following information:

Scene name - if blank/unchanged will use "default" naming scheme.

Y min clip

Y max clip

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We could also bring other key settings forward such as what entities to load, ESS, Octree/BVH to use, etc. Which could act as good reminders to the user to consider these options.