Use Streams in JpaRepositories

[iakunin]

• https://www.baeldung.com/spring-data-jpa-pagination-sorting
• https://www.baeldung.com/spring-data-jpa-query

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• All the Set<> and List<> must be replaced with Stream<>.
• Also proper exception handling during stream processing is required (will be done in #93).

[0pdd]

@iakunin the puzzle #205 is still not solved.

[0pdd]

@iakunin the only puzzle #205 is solved here.