Rename `booleans` Concept Exercise to use story/theme

[ErikSchierboom]

In the beginning of v3 development, Concept Exercises were named after their Concepts. However, we've later on changed this to have the Concept Exercises be named after their story/theme.

The booleans Concept Exercise should be updated to use a story/theme-based name and slug.

See https://github.com/exercism/v3-launch/issues/49