Add checker to control when a host has an outdated trento version

[rtorrero]

Following up on PR #198 it would be much more usable to have a checker that warns the user when a node is running an older trento binary.

The tricky part here is to guess what to compare it to. If I have understood correctly how checkers work, they run local to each node so we'd probably need to expose a version endpoint in the web server that the checker can check against to issue a warning in case there is a mismatch.

Other ideas are welcome too :-)