This change fixes #314:

• replaces slf4j-simple with logback in the project's dependencies;
• includes logback's optional dependency (janino) which is necessary to enable the use of conditionals inside logback.xml.
• updates the version of slf4j from 2.0.0 to 2.0.9.

After executing mvn clean package, please confirm that the package slf4j-simple is no longer listed as a dependency for the project by running the following command to confirm:

mvn dependency:tree -Ddetail=true | grep 'slf4j-simple'
[INFO] +- org.slf4j:slf4j-simple:jar:2.0.0:compile <---- ONLY on master, nothing should appear in this branch

If it is still listed, slf4j will issue the following notice and default to slf4j-simple instead of logback:

SLF4J: Class path contains multiple SLF4J providers.
SLF4J: Found provider [org.slf4j.simple.SimpleServiceProvider@309e345f]
SLF4J: Found provider [ch.qos.logback.classic.spi.LogbackServiceProvider@56a6d5a6]
SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation.
SLF4J: Actual provider is of type [org.slf4j.simple.SimpleServiceProvider@309e345f]

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  mvn clean package 
  ./bin/generate-samples.sh
  ./bin/utils/export_docs_generators.sh
  

  Commit all changed files.
  This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master.
  These must match the expectations made by your contribution.
  You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/python*.
  For Windows users, please run the script in Git BASH.

/claim #314