Clean-up all uses of getDet

With functional access to conditions, we need to remove the accesses to getDet in the code. I counted 111 cases in 83 files today, with very different cases:

• use of getDet in a functional algorithm: simple case, use functional conditions (LHCb::DetDesc::usesBaseAndConditions) and get the required detector element in the operator() directly
• getDet of a detector element in a Tool or Algorithm: inherit from LHCb::DetDesc::ConditionAccessorHolder if necessary and change the member containing the DetElement to be a condition accessor
• getDet in initialize used to create a cache -> previous step + add a derived condition