- Add `avatar_url`, `description`, `git_ssh_url`, `git_http_url`,
  `path_with_namespace` and `default_branch` in `project` in push, issue,
  merge-request and note webhooks data
- Deprecate the `ssh_url` in favor of `git_ssh_url` and `http_url` in
  favor of `git_http_url` in `project` for push, issue, merge-request and
  note webhooks data
- Deprecate the `repository` key in push, issue, merge-request and
  note webhooks data, use `project` instead

Signed-off-by: NDmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

It seems that ruby can handle 'nil' value but other json processors
(like PHP) throw an error. This is always generated for empty arrays.

1) Adds a DB migration for all services to toggle on push, issue, and merge events.

2) Upon an issue or merge request event, fire service hooks.

3) Slack service supports custom messages for each of these events. Other services
not supported at the moment.

4) Label merge request hooks with their corresponding actions.

* add git_http_url and git_ssh_url to project web hook
* add visibility_level to project web hook
* add documentation about project visibility_level in API

Also execute GitLab CI on creating tag via UI