feature: added option to close an issue

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
feature: close issues on github

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
feature: close issues on bitbucket

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
feature: close issues on gitlab

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
improvement: check bitbucket response when closing issue

... the idea being, that bitbucket should confirm the status we gave to the issue.

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
improvement: check github response when closing issue

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
give the user some feedback when an issue is closed

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
added test for issue_close on all providers

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>