add gitlab gem to dependencies

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

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
adjust the gitlab host endpoint based on the repository in .git config

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
gitlab: add support for detecting the project's id

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
improvement: gitlab: only detect project id once, then reuse it

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
feature: add support for listing issues from gitlab

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
feature: gitlab: add support for creating issues + clarify delete actoin

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
add gitlab support for listing, creating, and deleting issues

resolves #6