Instead of calling the get_comment() we now have a callback for click,
that's called to validate and transform the given comment id into a
Comment object from JIRA.
This needed changes in showing an issue's comments, because we want to
make it easy to target a specific comment and therefore we need to show
the comment id.
If the user doesn't provide a comment id, we show a list of comments and
let the user chose the comment to edit/delete.
--jql can now provide filtering in addition to the other command line
arguments instead of replacing the whole query. This still allows the
same behavior as before by specifying none of the other options.