Refactor versions methods in ICS03

[adizere]

I think it would be nicer if these two methods get_compatible_versions() and msg.counterparty_versions() both return domain type objects Vec<Version> (instead of vector of strings). Then we can also avoid doing the conversion inside pick_version, and pick version would only be concerned with the logic of computing intersection and picking version.

Originally posted by @adizere in informalsystems/hermes#388 (comment)

I agree. Started to do the changes earlier but they are more involved and was thinking to do it in a separate PR. However if you feel I should do it here let me know and will start on it.

Originally posted by @ancazamfir in informalsystems/hermes#388 (comment)

[ancazamfir]

Closed via informalsystems/hermes#449