Load scenarios from JSON after professions.

Reading JSON files is a breadth-first-search, so moving the
scenarios.json file deeper into the data/json/ directory tree, we ensure
it loads *after* data/json/professions.json.

Fixes #8871 and also *correctly* fixes #8837.
Make JSON load order sane (explicit BFS).

The previous way of searching for JSON files was an unholy mix of stacks
and things that were acting more as a pre-order DFS, which made it hard
to express the correct JSON loading order.

Made into a BFS, so that depth (distance from root) will be the only
determinant of load order, as the intention seemed to be.
Merge pull request #8876 from narc0tiq/scenarios-after-professions

Load scenarios from JSON after professions.