Challenge documentation should move to challenges itself

[nbaars]

The asciidoc code within challenge.html should be simplified. We can move this to the Challenge classes. This way the decision is no longer in Thymeleaf removing

<div th:if="${ environment =='gcp'} and ${ challengeNumber  &gt; 8} "
         class="explanation">
        <div th:replace="doc:challenge__${challengeNumber}+'-gcp'__.adoc"></div>
    </div>
    <div th:if="${ environment !='gcp'}"
         class="explanation">
        <div th:replace="doc:challenge__${challengeNumber}__.adoc"></div>
    </div>

[commjoen]

I guess this can best be done when #35 and #40 are done :), as this kind of interacts with both