AthenaServices+AthenaKernel: Load persistent dictionaries in initialization.

During initialization of AthenaOutputStream, we are already loading dictionaries for classes that we write. This is to avoid issues with dictionary loading when multiple threads are running (ATEAM-697). But we can have the same issue with persistent (_p) classes. So load dictionaries for those too, if appropriate.

In the process, add AthTPCnvSvc::t2p_cnv_unique, which returns ownership to the caller, and which doesn't print any warnings on failure