Add FakeBkgTool from TopCPToolkit to CPAlgs
This takes the FakeBkgTool implemented in TopCPToolkit and adds to the common CPAlgorithims.
I believe @nbruscin is the original author of the TopCpToolkit code. Please comment if there is something we should be aware of. Also feel free to add your name at the beginning of the relevant files, or let me know if I should do so.
Tagging also @tgosart and @jmkelly who will help follow up on the MR and will use the tool once it is implemented.