Switch from Cobertura to Jacoco for test coverage

Cobertura can't handle Java 8: https://github.com/cobertura/cobertura/issues/176

We should switch to JaCoCo and start setting some test coverage goals.

Notes:

• Set test coverage to 40% (not enforced yet: some modules have even less)

• Remove Cobertura

• Remove cobertura:cobertura in Jenkins

• Generate Jacoco reports in Jenkins

• Maven verify will generate Jacoco coverage