FEATURE: trophy room

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Acceptance criteria:

• [x] "Trophy Room" main menu option renamed to "Discoveries"
• [x] Remove the conditionals from where we populate the main menu (along with any other vestigial cruft)
• [x] discovery.tscn exists on disk and can be loaded into
• [ ] Some kind of appropriate, nice-looking background (may be static in 1.0 to save labour). (Maybe steal ideas from the intro to Cabinet Of Curiosities)
• [ ] A scrollable list of discoveries is shown to the user. Ones that have not been found yet show as ??? instead of a name
• [ ] Discoveries are enumerated from the JSON files. (Early previews of this feature are allowed to hardcode the list to help with getting the UI right.)
• [x] When the user scrolls to an already-discovered entry in the list and presses [enter] or XBox (A), the background blurs, the mesh of the discovery is shown in the foreground, and a scrollable box containing the flavour text is show next to it. (For 1.0, the text may be scrolled in pages if that's easier to implement.)
• [x] While in a given discovery's "drill-down" view, [ESC] or XBox (B) should hide the mesh and flavour text and take the user back to the discovery list, ideally with some kind of effect (for 1.0, this may be as simple as we can get away with).
• [x] [ESC] or XBox (⬅Back) should take the player back to the main menu.
• [ ] Heroic, orchestral 4/4 time BGM containing the leitmotif from Undersea Canyon
• [x] Graphical key/button callouts should be shown at the bottom of the display
• [x] Audio effects for moving the cursor, accepting, or cancelling should play as appropriate (make consistent with main menu)
• [x] Trophy room should be 'dumb' and not need to know or care about the rest of the game's existence or state
• [x] Parchment background for the flavour text off to the right (covered in 3b188de2617)
• [ ] Refactor DISCOVERY.gd (comes very close to being its own story in terms of scope)

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background blur: https://godotshaders.com/shader/simple-blur/

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https://godotengine.org/qa/5175/how-to-get-all-the-files-inside-a-folder <-- enumerate all files in a given dir example code

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Some bits will need to be thrown out and recoded - I mistakenly thought it was possible to enumerate the files in a .PCK - this is, as far as I can tell, unsupported in 3.5.

The original idea was to try to make it easy to contribute new Discoveries without recompiling. I still think this is a good idea, but it's going to have to wait until after the conference. What's going to happen in the interim is:

1. We'll declare a Dictionary somewhere that lists all the Discoveries, along with their flavour texts (and maybe throw together some kind of script to convert a comma-delimited text file to the proper format).
2. Have an array of bool somewhere (with the same number of elements as the Dictionary from step 1) to track whether each discovery has been seen at least once or not, and maybe a second one to handle whether it was photographed or not.
3. Instead of having Discovery be a separate class, we should just have each one inherit from Spatial, and in a collided-with-player signal handler, set the appropriate bool out of table in step 2 to true.
4. On save, write out the array of bools to disk.