They're only used once each, and they're easy to build in-place.

Closes #1263, #431

Remove emphasis from system notes to avoid Markdown conflicts in names.

This MR extends the commit calendar so it searches for commits made with every email address the user has associated with his account.

This fixes one of the problems mentioned in gitlab-org/gitlab-ce#1162 and makes the behavior of the commit calendar as described in the profile.
"All email addresses will be used to identify your commits."

Add checkboxes to the application settings page for restricted
visibility levels, and remove those settings from gitlab.yml.

Normalize output to use:
- User name instead of username
- Include first line of title in message description
- Link to "Issue #X" instead of "#X"

Supports four different event types all bundled under the "note" event type:

- comments on a commit
- comments on an issue
- comments on a merge request
- comments on a code snippet

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.