Add scram tests.

Use with `scram b runtests`.  This runs `test/verify.sh` with three
configurations: ttl, tll_os, tll_ss.
We don't use subdirectories anymore.
Add branches for impact parameter et al.
Fix up MVA configuration.

Fix plotting the BDTG, and save MVA output to a log file again.
Implement printing the MVA variable ranking.
Keep cluster configuration and results grouped together.

As a side-effect, the `test/` directory is for testing only now.
Update ignores.
Add a Z-peak veto for the dilepton system.
Fix isolation based selection in the ditau channel.