API: Ability to filter milestones by state

Ability to filter milestones by `active` and `closed` state.

* Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/14931

See merge request !3566

Expose badges

This MR exposes badge somewhere in visible place.

![expose_badges](/uploads/d2e290d3013d1ef2b1bdeebbbe2c5d8b/expose_badges.png)

Closes #13801

See merge request !3326

Allow SAML to identify external users and set them as such

Related to #4009

Fixes #14577

This allows SAML to retrieve group information form the `SAML Response`
and match that to a setting that will flag all matching users as external.

See merge request !3530

Wiki preview URL converting problem [via Markdown]

Current implementation when rendering the preview, thinks relative links are for project repository files.

We are creating a new preview route that will define correct context data to render for wikis instead.

Fixes #2380, #1184

See merge request !3461

Unblocks user when active_directory is disabled and it can be found

We implemented a specific block state to handle user blocking that originates from LDAP filtering rules / directory state in !2242. 

That introduced a regression in LDAP authentication when Active Directory support was disabled. You could have a scenario where the user would not be temporarily found (like a filtering rule), that would mark the user as `ldap_blocked`, but will never unblock it automatically when that state changed.

Fixes #14253, #13179, #13259, #13959

See merge request !3550

Fix header link rendering when containing numbers

This fixes the problem where Markdown such as:

    ### 31st

Would get rendered as a link tag pointing to issue number 31 inside a
header tag.

See gitlab-org/gitlab-ce#14936 for more information.

cc @rspeicher 

See merge request !3568