GaudiAllen: actually filter events + fix tests
make mdf_write test actually tests if events are filtered + conditionally write events based on allen decision
Need: Allen!1165 (merged) MooreAnalysis!116 (merged) MooreOnline!216 (merged)
The issue: when using GaudiAllen to filter some mdf files (as in the allen_mdf_write test) the output file is always containing the same number of events as the input file. This is due to allen decisions not being properly propagated to the controlflow and as a result MDFWriter being called unconditionally. This is not detected in the test for 2 reasons: the test was not testing if at least one event was filtered out (only testing that at least one event was kept), and the default allen sequences we use in tests have a 100% efficiency due to the passthrough line prescalers being set to 1 by default. This MR and the corresponding Allen MR introduce a new Algorithm that collect allen decisions and propagate the decision to the control flow, when inserted before the MDFWriter, it effectively condition it. The Allen MR also change the default passthrough prescaler to not make all events pass.