Definition of critical files

[KilianKrause]

In the GetCriticalFilesController we offer two endpoints that compute "critical files". We should either define what we mean when talking about "critical" files, or we should provide an API, so that users can define those critical files themselves.
This could be one of the following:

• allow the user to define file patterns, e.g. include *Service.java and exclude *Exception
• declare only those files as critical, when certain metrics have a certain value, e.g. loc or cyclomaticComplexity