Gaudi Usage Improvements, master branch (2019.12.18.)

This is meant to make the introduction of the ConfDB2 file handling a bit safer...

To be able to use the latest CMake code with older nightlies / Gaudi versions as well, I updated the CMake code to produce empty .confdb2_part files when genconf is not producing one. Then I had to update mergeConfdb2.py to be able to deal with empty files. While I was at it, I also taught it what to do when it encounters a file containing gibberish. (Though one could very much argue that maybe the script should just die in that case...)

I also taught FindGaudi.cmake how to detect the version of the Gaudi installation that was found. At first I thought that I could use that version to switch between expecting or not expecting ConfDB2 files to be made by genconf. But it turns out, the (reported) version of Gaudi did not change when this feature was introduced. 😦 Still, I thought this would be a nice feature to keep.

Tagging @leggett, @wlampl and @fwinkl, just so you'd be aware of what's happening.