Add support for selection of IP version to be used in connecting

[ppb2020]

In preparation for the connectbot Android app to be able to restrict connections to IPv4, added a complement of new connect() methods with different signatures.

• Kept the versions with the original signatures for backward compatibility.
• Added a multitude of complement signatures to cover all combinations.
• Only needed one new signature for connectbot, but nonetheless created all possible combinations of signatures, for completeness.
• Did not do the same for the initialize() method as it is mostly internal.
• If backwards compatibility is required for this method as well, a simple change can be made to re-add the original method calling the new one.

As a side note: had to play with Java and Gradle versions to make things work for me during testing. I did not submit these changes as I do not wish to affect the current builds. Hence, the commit herein is missing some of the changes I made during testing and therefore the changes are nominally untested against the current versions. This should not be an issue as the changes are straightforward.

Once this is integrated and the new version is used by connectbot, I have changes to connectbot that will take advantage of one of the new signatures.

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