Add test of bs decoding
This tests configures BS writing by hand in egammaRun test and adds a test that wollows with docoding of the produced BS. Together they test serialisation/deserialisation chain as well as filling up the missing collections in case when, due to the rejection they were absent in BS. The next step in this domain is to struture better configuration. A novelty in tests is that BS decoding depends on egammaRunData - will see how it works in CI.