Refactored  the csp-logger to work as a module as well as standalone app

When used as a module, it can inform the nodejs app about violations directly while, or instead of, logging.
The biggest change here is to remove assumption that the configuration is known at the time of initial run of all the code. It can now be configured at runtime.

I also added an entry point to work as a commandline app (if this gets published to npm, one can just `npm install csp-logger` and run it in terminal.

Once you merge the pull request, you could publish the module to npm. (I won't attempt versioning the published script, it's something only an official maintainer should do)