Rethink / remove midnode's detail_fetched about oztree HOT 2 OPEN

The above commit gets rid of my populate_ott_name_map bodge that started this issue, and setting detail_fetched instead, but the rest of the points here still stand. ott_name_map is pretty likely useless.

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This was an interesting thread to pull. There were 2 cases where ott_name_map came into play:

• On leaping to search results, we didn't wait to fetch details first. The search results were stuffed into ott_name_map so at least the node names were available
• On tree startup, node metadata could be fetched, but details_fetched wasn't set. We refuse to return the metadata in this case, but ott_name_map doesn't have similar qualms. I haven't discovered entirely why this would be the case, but checking if the metadata is available (array lookup) isn't dramatically more expensive than checking details_fetched.

id_ott_map has become redundant in exactly the same way, so gotten rid of that as well.

Generally, I suspect everywhere details_fetched touches could do with a rethink.

• Cache a reference to data_repo.metadata.leaf_meta[this.metacode] rather than caching metadata in the midnode object. Things like get sponsor_name() just become an alias to get_metadata.
• Push any modification of cached values (e.g. capitalizeFirstLetter) further upstream, at least to the metadata-parsing.

I wouldn't be surprised if it evaporates. But this is probably enough wild refactoring for today.

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