Centralize all references to Database Tables

[Populustremuloides]

Currently, multiple lines of code across many many files in different folders reference tables in the database for the strings that execute SQLite code. This becomes problematic when we make adjustments to the tables in the database; it's not always easy to make sure every reference to a particular table has been changed. Having a centralized file declaring variables which store strings that are the names of the tables in the database, and using those variables in place of "magic strings", will solve this issue.