BuildFile.addDependencies(...) should not add existing dependency again

[fabapp2]

To reproduce:

• apply migrate-jpa-... (adds spring-boot-starter-data-jpa)
• apply migrate-stateless-ejb(adds spring-boot-starter-data-jpa again to resolve @Transactional)

BuildFile bf = retrieveBuildFile();
bf.addDependency(Dependency.builder()); // e.g. add `foo:bar:1.0`
bf.addDependency(Dependency.builder()); // e.g. add `foo:bar:1.0` again

will add the dependency foo:bar:1.0 twice

[fabapp2]

Currently, the implementation will add a dependency with compile scope when the same dependency already exists with test scope. It should merge these dependencies and set the state accordingly (or throw exception?)
in #455