Fixes incorrectly called 'version' property in the _log_version_number() method.
Adds a 'classes' directory and index files in the main and 'classes' directories.
Adds a basic admin screen skeleton.
Adds logic to register and output settings sections.
Separates the settings logic into it's own class, and sets up a skeleton for rendering the settings screen fields.
Adds basic settings save logic.
Makes sure the description is displayed correctly for checkbox fields.
Adds basic settings validation logic to the settings class.
Adds markers to the main class to denote where admin-related items start and end.