CompFactory: namespace access for legacy Configurables

Frank Winklmeierrequested to merge
fwinkl/athena:fwinkl_20211019T104322 into master

Implement attribute lookup for Configurables within a namespace for the legeacy CompFactory. This allows to write code like

alg = CompFactory.NS1.NS2.MyAlg()

that works in the old and new-style configuration.

Also implement unit test for CompFactory.

cc @tbold @wlampl

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