Refactoring of god-classes (AbstractMetric/PluginInfo)

For the software reengineering course, we focused on violations of the Single Responsibility Principle. Two clear examples of this are the AbstractMetric (god) and PluginInfo (god/schizophrenic) classes. Tests were written for the original classes, after which the classes have been refactored, and finally the tests adapted again. 
More extensive information about this commit can be found in our documentation here:
https://github.com/Venorcis/Alitheia-Core/blob/master/report2/README.md