Gitlab-to-Pad

Add tree.py, modify utils.py and cli/gitlab_to_pad.py to enable pulling issues from gitlab and posting a proto-protocol into a hedgedoc note

utils.py now supports trees of issues (class defined in tree.py) with which issues blocking other issues will be handled and outputted accordingly

gitlab_to_pad.py now relies on hedgedoc.py to implement a functioning overwrite_note() function.

Introduces the following new mandatory environment variables:

GITLAB_URL - the url of the gitlab instance

GITLAB_TOKEN - the private access token to the repo

GITLAB_PROJECT - the id of the repo

GITLAB_ISSUE_BOARD_ID - the id of the issue board according to which the issues are sorted

PAD_TEMPLATE_PATH - the path to the template for the hedgedoc note

MEETING_TIME - the time of the meeting

MEETING_DATE - the date of the meeting

MEETING_LOCATION - the location of the meeting

HEDGEDOC_URL - the url to the hedgedoc note

LABEL_SLEEPING - the label used to identify sleeping issues

LABEL_TODO - the label used to identify todos

Introduces the following new optional environment variables:

LABELS_HIDE (csv) - these labels will not be displayed in the output

LABELS_EXCLUDE (csv) - any issues that are marked with one or more of these labels will be excluded from the output