Improve test applications

Previously, the test application all worked slightly differently and
output all results to an HTML page.  This meant that using them for
automated testing wasn't viable.  This change updates the applications
to return JSON payloads from REST endpoints.  It also unifies the
actual functionality into a single "core" module which is then
delegated to by the various application web tiers.  Finally, this new
setup has illustrated bugs in Spring Boot (--local is not working) and
the groovy application isn't quite working yet either.

[#58925744]
Merge 58925744-improve-test-applications to master

[#58925744]