Move sources to the standard Gradle layout

Pure file moves, no content changes: every rename is 100% similarity.
Verify with: git show --stat -M100% (1,806 renames, 0 insertions,
0 deletions). Java sources to src/main/java, resources to
src/main/resources, tests to src/test/java and src/test/resources,
in every module (donkey already used this layout).

Refs #52

Signed-off-by: Finnegan's Owner <44065187+pacmano1@users.noreply.github.com>

Author: pacmano1