Refactoring: coalesce use-*-* goals.

[andrzejj0]

I wanted to try and do something similar to what #292 was, but since the plugin has moved on, it first needs some refactoring.

This PR makes the use-*-* goals use shared codebase in order to make future refactoring simpler.

[slawekjaranowski]

why such ...

[andrzejj0]

This is called by a method from the base class, UseLatestVersionsMojoBase#update so that it selects snapshots -- we are looking for snapshots to upgrade to:

                Optional<ArtifactVersion> newestVer = versionProducer(Arrays.stream(versions.getNewerVersions(
                                dep.getVersion(), unchangedSegment, isAllowSnapshots(), isAllowDowngrade()))
                        .filter(this::artifactVersionsFilter));

So, to make this execution universal and common to different sorts of "use-*-*", the method in the base class uses those callback methods.

As an alternative, this could be done using composition and an object having those parameters (allowSnaphots) as its constructor parameters.

[andrzejj0]

The property allowSnapshots doesn't make sense in some of the goals, like this one (because here we are only interested in snapshots, so we must allow them), so I'll push the property down the class hierarchy to goals where it does make sense. At the same time, I'll pull isAllowSnapshots() upwards as an abstract method.

[andrzejj0]

Please note that I'm doing this in stages so that the PR doesn't grow too big.