We can inject plugin, repositories and dependencies directly from
the top-level build.gradle.

This extracts a common version of junit for all projects (and
updates anagram to use assertj, the junit matchers did not work
with 4.12).

An anagram is defined as

1. the same letters
2. rearranged
3. to make a new word

The existing assertion only checked the presence of the expected word,
but did not explicitly exclude the existence of results that match the
input exactly.