support for list of tools and add tools to CaloFutureMergedPi0

Fixes #108 (closed) by looking at existing functionality to treat lists of DataHandles or Algorithms and doing similar.

Dear experts, please take a look whether the changes make sense, especially please check _inputs_from_tool as I did not fully understand what it is doing and what I was changing there.

I tested that this implementation works correctly when adding the list of tools to CaloFutureMergedPi0 as discussed in MR !282 (merged) (in a sense that the counters are the same as in Brunel). However I did not want to push it to the same !282 (merged) which I hope is ready to be merged, in order to not delay it. Once that MR is merged, it will be possible to update the tests with calo algortithms in this MR, while so far one could only review the new functionality but cannot see that it works.