[MRESOLVER-461] Cleanup in dep managers

[cstamas]

3 of them were almost same.

• default: derives to infinity, always applies
• transitive: derives to infinity, applies after depth>=2
• classic: derives until depth>=2, applies after depth>=2

Note: "derives" means picks up depMgt from currently processed node. Hence, classic ignores all depMgt in graph coming from transitive dependencies. depth=1 is root (ie. project), depth=2 are first level deps (those listed in POM), etc.

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https://issues.apache.org/jira/browse/MRESOLVER-461

[michael-o]

There is no logical change, but only pulled up to a super class?

[cstamas]

Yes, a cleanup

[cstamas]

thing is: will do resolver - maven - IT run to test classic, but other two was never tested (so i can be only certain did not break them). Will also add UTs as only classic has rudimentary one

[cstamas]

OK, the resolver master - maven master - maven IT master ran OK, so this shows that "classic" was undisturbed.

Next will do UTs and will merge this as I have your approvals.

[cstamas]

Removed ClassicDependencyManagerTest and added new DependencyManagerTest UT tests all 3 of implementations (all aspects, not only Optional as Classic UT did) with comments sprinkled explaining what they do.