Factor out location code for initialization and updateTurretPosition()

All the turret classes extend from Turret, so we can reduce some code
redundancy by factoring out the locX = x in init for all the turrets
and removing the updateTurretPosition code unless it needs to be
overridden.
Merge pull request #1 from kevinlondon/master

Factor out location code for initialization and updateTurretPosition()