Apply singleton pattern for all class instances used in main

**Why?**
To clean up & make the source code much more readable. Also will shorten the list of places in which bugs can occur.

**How?**
The singleton pattern should be applied to all of HearSay's custom modules (essentially *.py excluding main). This will 

**Anything else?**
[Python singleton reference](https://python-patterns.guide/gang-of-four/singleton/#a-more-pythonic-implementation)