Create config helpers for coverage plugin paths and tasks

[vmasek]

Create config helpers for coverage plugin paths, where they would support specifying multiple targets so we can do test, integration-test, or whatever else.

• coveragePathsFromAllNxProjects
• coveragePathsFromNxProject
• coveragePathsFromNxProjectAndDeps

But we will also need to run the test (coverage) targets for the libs too, so the command needs to be more clever too, probably with similar helpers.