gradle: build the projects with Gradle (v4)

Signed-off-by: Ferry Huberts <ferry.huberts@pelagic.nl>
gradle: add a (temporary) script to fully exercise the build

I keep having to look up all the targets...

Signed-off-by: Ferry Huberts <ferry.huberts@pelagic.nl>
cnf: gradle: add class cycle checks

Signed-off-by: Ferry Huberts <ferry.huberts@pelagic.nl>
build: gradle: add p2 generation

Signed-off-by: Ferry Huberts <ferry.huberts@pelagic.nl>
gradle: add 'p2' and 'dist' to the script to fully exercise the build

Signed-off-by: Ferry Huberts <ferry.huberts@pelagic.nl>