Transform the Actives class into an array-like class
Transform the Actives class into an array-like class

Updated the Actives class (`./src/classes/actives.js`) such that it
becomes an array-like class with array-like properties such as:
- Elements are stored directly on this using an auto-incrementing index.
- Additional methods which you expect to find on an Array, such as
  `.sort()` and `.splice()`.
- A `length` attribute.

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