Add a copy of GaudiAlg (imported from Gaudi v37r2)
In the grand plan of removing GaudiAlg from Gaudi (see gaudi/Gaudi!1444 (merged)) we need to have it available in LHCb and built if it is not imported from Gaudi.
This MR adds a copy of GaudiAlg imported from Gaudi v37r2, slightly modified to be transparently enabled if the copy in Gaudi is not built.
Note: since LHCb still uses clang-format-8 and YAPF, I had to reformat the code, but the commit should be reverted if we merge !4346 first
Edited by Marco Clemencic