Add concept: `maps`

[sanderploegsma]

The goal of this issue is to add a new concept to the Java track that introduces maps. The corresponding concept exercise can probably be based on the "High Score" exercise from the Elixir track.

Instructions on how to contribute to the Java track and how to implement concept exercises can be found in the contributing guide.

As always, leave a comment here if you want to work on this exercise, and we'll assign it to you. In case you have any further questions, feel free to ask here.

[sanderploegsma]

A note on naming the concept exercise: since there is already a practice exercise named "High Scores", it might be worth considering renaming the exercise when porting it from the Elixir track to avoid confusion. This also means that we have to make sure the exercise glyph is available with the new slug.

[sanderploegsma]

After adding the concept, it should be added to the prerequisites in the config.json for the following practice exercises:

• Go Counting
• Nucleotide Count
• Palindrome Products
• Parallel Letter Frequency
• SGF Parsing
• Word Count
• Word Search

[smcg468]

Happy to work on this one

[sanderploegsma]

Great, assigned. Have fun building! 👍