* Commented out bad code in DatabaseManagerCustomers.cs that was preventing compiles
* Added SelectQueryBuilder class for simplifying SELECT statement construction for use in DbCommands
* Added ModificationQueryBuilder class for simplifying INSERT/UPDATE statement construction for use in DbCommands
* Added the AccessCode enum and documented its rationale/use
* Changed Employee class to be non-abstract, so instances of it can be used just for data transfer. The "Add New User" workflow will require an Employee object but the 'type' of employee won't be known from the start until the user sets it
* Implemented the 'core' DatabaseManager.cs code, so that we can open and connect to the DB file
* Implemented the DatabaseManagerEmployee.cs code to show how to create our Add/Edit/Get DB methods
* Added an "InitialSetup" class which needs to be ran at startup when using a fresh DB file. It is where code to auto-fill the DB with given data is found/added
* Can't actually run the App right now due to the Program.cs changes (you would have to comment out the InitialSetup code), and...
* TODO: The DB tables need to be recreated yet again, as their Identity properties weren't set. Without them, we're forced to generate record IDs ourselves on INSERT. The only table which shouldn't have an Identity setup is the AccessCode table as we populate that ourselves.