Don't need to instantiate these off the bat

  - Have our BaseSite create its own SiteManager if None is specified.
Very rough first cut of core tracker interactions.

  - Addition of other very vital fields to the Fuel table.
  - Need a more elegant way to abstract away the primary keys.
Remove user specified reinforcement field.

  - In practice this is probably not specified on a per tower basis.
Ensure that the site is torn down after use.

  - Just set it to nothing.
Reimplement target strontium level calculator.

  - The target strontium level is now specified using the optional
    parameter for that purpose for the related methods.
Integrate the tower management into the tracker.

  - The sql based tower class now extend from the base tower class.
  - TrackerBackend is now able to serve as the manager for all the pos
    tracking classes, so it can add towers.
  - Persistence can be achieved now.