Less comments and per job success/failure messages

This PR introduces a "useDetailedComments" flag: originally when plugin misses rights to changing PR status, it replaces it with comments, leading to many spam emails. This flags silences those emails, leaving just the success/failure ones.
It also introduces per job success/failure messages: it's also possible to use jenkins environment variables in those comments, as they get expanded.
Such comments are sent based on the state of the build and no longer on the presence of a publishedURL.