add first version of ReadDecorHandle to AnalysisBase

Just the next in the list of data handles we need.

Please note that this has a bunch of commented out code. The new data handle is copied over from the existing data handle in StoreGate, so anything that I didn't need right away I kept, but commented out. The plan is to first finish the porting, make the code that's needed work and then go through the remaining commented out code, and decide what of it to keep/implement and what to remove.