Added support for configuring Pages CNAME and TLS Certificates

Preliminary implementation with all expected features that will ship with this feature.

What is supported:

- Multiple domains per-project
- One certificate per-domain
- Validation of certificate
- Validation of certificate chain (solves a problem with missing intermediates)
- Validation of private key against certificate
- Support for Pages Daemon (the shared/pages/group/project/config.json) that will be read by daemon

Plans for enhancements:

- [x] Write behavior and unit tests
- [x] Make the UI nicer

/cc @grzesiek @DouweM @sytses @rspeicher @marin @jacobvosmaer

See merge request !173

This reverts commit 0bb6c63b19f3574735838190b415a8b37eca3900.

This reverts commit 1e4f43e854b3dda901ee6d3469153ea72c75959f.

1. PagesController is used to show all domains and general overview of Pages
2. PagesDomainsController is used to manage pages domains

CE upstream



See merge request !183

Fix Weight display in Issuables' collapsed sidebar

Fixes #284.

/cc @jschatz1 

### No weight set

![Screen_Shot_2016-02-15_at_16.02.59](/uploads/3a46684f90531fe1e319a17147272c10/Screen_Shot_2016-02-15_at_16.02.59.png)

---

### Weight set

![Screen_Shot_2016-02-15_at_16.03.18](/uploads/24accd1e795d16f4802ea1f0fe98f588/Screen_Shot_2016-02-15_at_16.03.18.png)

See merge request !184

Fix undefined method `postgresql?` during migration

See merge request !2820

Improved LDAP documentation about the use of multiple servers [ci skip]

cc @ernstvn

See merge request !177

[ci skip]

Add notice about offline migrations

/cc @sytses 

See merge request !1723