Fixed de-serialization of MembershipSourceType by letting the JacksonJsonEnumHelper know that the first letter should be capitalized

This makes it possible to stream data coming
from another server straight into the POST request to Gitlab,
saving an extra, expensive, and useless IO operation on disk.

Fix #769

Adding branches_to_be_notified to SlackService and deprecating notify_only_default_branch as per
https://docs.gitlab.com/ee/api/services.html#createedit-slack-service

A 'scope' attribute was added to the Events API that allows retrieval of all events for a user across all the projects that user has access to.  This change adds support for this new attribute.

Ensuring test SystemHooks are removed if tests fail, adding commentary/todo to address GitLab issue at future date

- readme_url
- can_create_merge_request_in
- import_status
- ci_default_git_depth
- remove_source_branch_after_merge
- auto_devops_enabled
- auto_devops_deploy_strategy
- auto_devops_enabled
- statistics.packages_size
- shared_with_groups.group_full_path

fix #613 #632 #667

Added option to preserve underscores in the JacksonJsonEnumHelper to fix TargetType.MERGE_REQUEST value. (#615)

Remove UserListSerializer and UserListDeserializer from approvedBy field in ApprovalRule (fixes #589) (#590)