Add jacoco maven plugin for generating code coverage reports

I have added jacoco maven plugin to generate code coverage reports.

Reports are added to `target/site/jacoco-ut/`

I had to configure `maven-surefire-plugin`, so it's outside of `maven-enforcer-plugin` now.

I have run test to check how it affects running time, command used: `mvn package  -Dmaven.test.skip=true -Djacoco.skip=true` and difference with or without jacoco was unnoticeable 

When you choose to generate code coverage the overall build process will take few seconds longer.
At other places, we're using version 2.12.4 of maven-surefire-plugin. Is there a reason for upgrade? If yes, please upgrade at all places at the same time.