HGBase Code (Desktop)

New method to check whether the specified path points to a valid audio file.

Removed code smells.

Formatted code.

Added a functional interface for a function which accepts three arguments.

Method to pick a random element from a list.

Removed code smell.

Generic methods to write/read a collection or a map to/from an XML file.

Added setter for first and second and constructor for empty pair.

Java doc corrected.

Documentation and formatting.