Record mechanism for IJetProvider -- ATLJETMET-1225

Restructured how IJetProvider returns the jet container it produces and add a record method to the IJetProvider interface. This has two benefits:

1. Avoid memory leaks of the aux container and remove all bare pointer handling. Previously it may not have been obvious that one would need to extract the store from the returned jet container and manage its memory.
2. Because some tools (!30790 (merged)) will create a different aux container type and we don't want clients to have to know anything about the implementation, we forward the WriteHandle to the IJetProvider, such that the record is handled there, and the creator can use the most derived aux container type for the record to StoreGate, avoiding any loss of information.

Since this is mostly about code transparency, I also did a little bit of interface cleanup.