State manager for the components theme.
Ensures that the content inside the SeniorDesignSystem widget follows the theme.
You must pass the initial theme as a parameter. If your application doesn't have a custom theme you can
the theme SENIOR_LIGHT_THEME or SENIOR_DARK_THEME which are the default themes provided by the library.
Discards any resources used by the object. After this is called, the
object is not in a usable state and should be discarded (calls to
addListener will throw after the object is disposed).