Add ability to use URL for the configuration file path

[Alexander-Krause-Glau]

I would like to host single instances of the configuration files (Checkstyle and PMD) in one public github repository instead of versioning the same file over and over again in multiple source code repositories.

There are obvious disadvantages when using this approach in projects with dedicated developers, e.g., small developer teams for seperated microservices. However, I reckon that this might not be the case in our research projects, where at most 5 people (most of them students) work on the same overall code base with more and more projects involved.

[Alexander-Krause-Glau]

Dunno if this is related to #46 .