Drop the DbCalcState

[sphuber]

The DbCalcState was used to both store the current state of JobCalculations, but also acted as a lock-mechanism, by only allowing progressive state changes. This last functionality is now the responsibility of the Runner. It is still useful to keep the job state, but this can now simply be furnished by an attribute. This also means that the specific IMPORTED state can be remove, since that is no longer applicable. It was supposed to stop imported calculations to be picked up by the daemon, since the old daemon determined which calculations had to be run, based on their DbCalcState.