Fixing #251: proper handling of InvalidSegmentException and InvalidVersionSpecificationException

[andrzejj0]

The situations indicated in the exceptions were not handled properly throughout the code, in some places, MojoExcecutionException was simply being thrown leading to the whole run being stopped; InvalidVersionSpecificationException was unchecked, leading to the same.

Handling those situations in the Mojo itself rather than in the methods so that a proper handling could be effected where necessary.

Because of all that, a rather sizeable refactoring was due.

More PRs will follow, I want to refactor and polish the code more, but this one is what's necessary for resolving this issue.

So, like I said in the linked issue:

The more I look into it, the more issues I see:

• segment appears to be 0-based (see e.g. AbstractVersionsUpaterMojo.determineUnchangedSegment or MavenVersionComparator.innerIncrementSegment), but the comparison against the segment count suffers from the 1-off problem:

if ( segment > segmentCount )
{
    throw new InvalidSegmentException( segment, segmentCount,
            version.toString() );
}

• segment determination flags (allowMajorUpdates, etc.) are actually not at all independent, but are actually a sort of enum; so an actual enum or an unchanged segment index would be better;
• part of the above: it's not actually possible to have allowMajorUpdates = true and allowMinorUpdates = false; allowMajorUpdates = true implies all others also being true;

There are probably more problems with this, but I'll limit the scope of this item to the issue OP raised only. The other findings will be done as separate issues.

[andrzejj0]

@slawekjaranowski please review 😄