Checkstyle for this project itself

[vorburger]

#153 has as discussion about having Checkstyle for this project itself (its source, not its users) ...

... and I'm personally all for "eating our own dogfood" here!

[vorburger]

@victornoel asked (in #153) :

should we start with a minimal setup with forbidding such thing or do you know of a checkstyle configuration that we could use as a starter?

if I get to chose 😃 then I vote for the one we use here in OpenDaylight.org - but I'm happy if someone wants another one as well!