Graphviz integration and persistence refactor

[alessandrocarminati]

This patchset includes several changes to a codebase, including:

• Introducing a new mock driver for persistence-related functions to decouple high-level function tests from the persistence layer.
• Adding support for C-style switchable debug messages.
• Fixing errors and improving the makefile.
• Making the external C parser optional for generateOutput and adding a dedicated test case for the parser itself.
• Introducing a small Flex-Bison dot parser for testing the Nav application.
• Refactoring Nav to include Graphviz functionality for diagram images production.
• Completing the test port for the newly refactored SQL component.
• Refactoring the SQL component by abstracting it with interfaces and receivers to make it easier to make changes to the persistence code down the line.

[alessandrocarminati]

Apparently this PR now needs to be rebased.

[alessandrocarminati]

Closing this PR and creating a new one with the rebased branch.