Warn when user wants to configure properties in way it is not fully supported

I was quite surprised that even i switched on checkstyle.configurationFile changes were applied for all file. I though this is sputnik error but it seems to be lack of support. I added some validation so nobody won't be surprised :)
I like this concept however I'm not sure if option shall be passed as parameter or get via singleton inside the method. Take a look and give comments.

I don't know how Stash is working and what is supported by this connector so I won't provide tests for this. Feel free to update.