[BZ 1120418] big refactoring for step calculator(s)

The only StepCalculator thus far is DeployCalculator. It had a lot of redundant
code for persisting steps. I never really liked having EntityManager and SLSB
calls in the step calculator. For one thine, it makes writing unit tests more
difficult. Persisting steps has been pushed up to
StorageClusterMaintenenanceManagerBean, which also now handles determining
whether or not steps need to be recalculated.