FakeBkgTools: LhoodMM_tools can now loop over systematic variations

Two small updates for the FakeBkgTools package:

• while the LhoodMM_tools class was originally not able to switch from one CP::SystematicVariation to the next, @evarnes had improved the tool at some point to overcome this limitation. However we had overlooked to remove the original protection against multiple calls to applySystematicVariation() (since it is now perfectly safe to do). The commit 12e4c898 fixes this, such that the feature can be used.
• the dual-use test executable used for continuous integration (fbtTestBasics.cxx) was extended in the commit 032ed518 to properly illustrate (and test) decorations of the EventInfo object to pass event-level information to the tools, following a recent discussion with @alarmstr (thanks!).