Resolve "Add functionality to define custom plot styles for Matplotlib plots"

The idea behind these custom plot styles for Matplotlib plots is to configure the plot style options in a separate file. This file can be generated by the init command. Plot styles that can be shared, may be added to a common folder for plot style file. These custom plot styles can be reused by providing the respective parameter to the plot functions to choose the plot style for the plot at hand.

Closes #178 (closed)