Change db connection to initialize in main, only have one connection instance

[Maria-Cordero]

The connection is currently being defined in every single model. Change to have the connection in main.

[igtampe]

ok so my proposed solution is the same as the one presented with the session manager. Make a singleton connection

Here's the thing:

And its implemented like so:

In our testing it managed to connect and return the empty list expected of courses. We disabled connection close:

And in our monitoring using the heroku dashboard connections did not increase

Let me know if this works so we can implement this literally everywhere else the DB is called