Shortened run() method for show command

as proposed in #76
Renamed methods for printing an issue

old print_issue() is now print_issue_summary().
old print_issue_completely() is now print_issue().

As proposed in #76.
Shortened printing full issue information

This patch changes the printing of the full issue information by
composing a list of labels by joining the labels into a new field inside
`issue` and using this one.