Various setup for join operator

This MR contains various changes and fixes as a basis for implementing the join operator. This includes:

• a dockerfile to build a container where broom can be run without the need to install anything manually

  docker build . -t broom
  docker run -it -v $(pwd)/src:/broom/src -v $(pwd)/scripts:/broom/scripts broom
  ./scripts/broom <...>

• configuration fixes so that qtest works and inline tests can be executed (dune test)
• moved some code from StateTable into the new modules Entailment and Join
• code to log joins (input+output) to a file, and a script to make this output a bit prettier

  diff --git a/src/biabduction/Config.ml b/src/biabduction/Config.ml
  index d12453c..985a649 100644
  --- a/src/biabduction/Config.ml
  +++ b/src/biabduction/Config.ml
  @@ -227,7 +227,7 @@ let print_contracts () = !_print_contracts
   let _dry_run = ref false
   let dry_run () = !_dry_run
   
  -let _log_joins = ref Option.none
  +let _log_joins = ref (Option.some "/tmp/joins")
   let log_joins () = !_log_joins
   
   let _use_legacy_join = ref true

  Then, use ./visualizeJoins.py /tmp/joins
• a config switch to switch between old and new join operator (both currently exactly the same)
  → use_legacy_join in Config.ml

As of now, this should not change anything about the functionality.