Sort featured July #12in23 exercises into the tree

[vaeng]

Users who chose to do learning mode can see the featured exercises in the tree.

I did all five exercises with the minimum of tools available and came to the sorting seen in the config.json file.

This is what I came up with:

Bob

• loops
• strings

Allergies

• classes
• std::unordered_set
• string
• const
• reference
• unsigned

Reverse String

• string
• const
• reference
• loops

High Scores

• Classes
• vector
• size_t
• iterators

Armstrong Numbers

• loops
• includes

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Some of these concepts are not yet in the tree, so I will make another PR to add to their instructions about what challenges may lay ahead of the students.

[vaeng]

I also removed some of the beta status for the exercises, so the non-maintaining user can see them.