Sorting refactoring

* refactor sorting logic for web UI
* refactor and document ordering for API: project, issues, merge requests
* explicitly define ordering in models using default_scope

See merge request !1476

Don't have Markdown preview fail for long comments/wiki pages.

See https://github.com/gitlabhq/gitlabhq/issues/8611.

See merge request !1479

Update smtp example to add openssl_verify_mode

See merge request !1478

See https://github.com/gitlabhq/gitlabhq/issues/8611.

GitHub importer refactoring

See merge request !1477

Submit comment on command enter

Fixes #1869.

See merge request !1474

Remove duplicates from group milestone participants list.

See merge request !1473

Gitlab.com integration && Gitlab importer

#1933

See merge request !1456

Fixes #1869.

add editor command to update database.yml; cleanup

Conflicts:
	CHANGELOG

Redirect signup page to signin page.

Resolves #1916.

See merge request !1468

Resolves #1916.

Disable reserverd project names

Fixes #1550

See merge request !1471

Because since project always belongs to namespace it dont need such
strict restrictions any more