Added support for creating both standard AOD and several deltaAOD's in the same

Added support for creating both standard AOD and several deltaAOD's in the same
ESD-based analysis. Producing a deltaAOD using AliAODHandler::SetNonStandardAOD()
in an analysis on input AOD is still possible. To use the new feature:
- use a standard AOD handler (no call to SetNonStandardAOD)
- in the AliAnalysisTaskSE-derived task, call AddAODBranch(cname, addobj, fname)
where the newly added fname is the file name where the branch(es) is(are) to be
written.

Added AliAnalysisTaskSE::IsStandardAOD() to check from the user code if the AOD
handler is configured for standard AOD or not. Check first via AODEvent() if there
is any AOD handler at all.