code readability improvements

remove obsolete code

ongoing work on `many-to-one` relationship implementation

move jacoco-maven-plugin configuration to <build>/<plugins> sections of the POM

integrate with codecov.io

integrate with codecov.io

reduce code duplication

make use of Lifecycle event wherever possible

polish implementation details

polish

preparing ground for many-to-one implementation

self-documenting code

further development of Relationships DSL

polish DSL internals

unit testing OneToManyRelationshipGuard