Add messageID from string and from parts

[addisonj]

If we want to deal with string message ids, we need methods for being able to create them from either a string or a using the individual parts of the message id.

This exposes some constructors for this as well as an equals method to make testing more straight forward (but I am not sure if we want to expose equals...)

This is primarily to match the java implementation, but if we don't want to add the string version, we should at least expose the method to make up a message id from the individual parts.

This commit adds tests for the needed new methods

[wolfstudy]

ping @addisonj any update for this?