Deactivate spring's propdeps plugin for now

It prevents execution of mains in the main sources. Issue opened on github.
Remove pom.xml
Update msg-simple dependency
Remove tests for JsonNodeReader

Different plan. This class will systematically "read fully". It will take an
ObjecMapper as an argument.
build.gradle: remove fatjar plugin, deactivate propdeps plugin
Re-introduce HTML test output
Fix javadoc links to work with Java 8's javadoc tool