Partially addresses #47424.

Remove order param from the MilestoneFinder

See merge request gitlab/gitlabhq!2259

(cherry picked from commit 14408042e78f2ebc2644f956621b461dbfa3d36d)

155881e7 Remove order param from the MilestoneFinder

This reverts commit e00fb2bdc2090e9cabeb1eb35a2672a882cc96e9.

# Conflicts:
#	.rubocop.yml
#	.rubocop_todo.yml
#	lib/gitlab/ci/config/entry/global.rb
#	lib/gitlab/ci/config/entry/jobs.rb
#	spec/lib/gitlab/ci/config/entry/factory_spec.rb
#	spec/lib/gitlab/ci/config/entry/global_spec.rb
#	spec/lib/gitlab/ci/config/entry/job_spec.rb
#	spec/lib/gitlab/ci/status/build/factory_spec.rb
#	spec/lib/gitlab/incoming_email_spec.rb

This reverts commit cb10b725c8929b8b4460f89c9d96c773af39ba6b.

Memoize Milestoneish#issues_visible_to_user and counts to reduce lookups
Milstoneish SQL optimised with project, but still slow on GlobalMilestone

This commit adds a number of _html columns and, with the exception of Note,
starts updating them whenever the content of their partner fields changes.

Note has a collision with the note_html attr_accessor; that will be fixed later

A background worker for clearing these cache columns is also introduced - use
`rake cache:clear` to set it off. You can clear the database or Redis caches
separately by running `rake cache:clear:db` or `rake cache:clear:redis`,
respectively.

The frontend will then always use the name as the ID - like previous

* Add Labels tab to Groups
* Add decorator for label so it's aware of Milestones.

With this change we avoid doing N+1 queries when viewing Milestone's
Issues/MRs from a Group context.

Make methods return ActiveRecord Relations instead of Arrays.

Closes #5908

Closes #4226

Two issues:

1. The constraints in the resources were incorrect. Here's what it was before:
```
group_milestone  GET /groups/:group_id/milestones/:id(.:format)  groups/milestones#show {:id=>/[a-zA-Z.0-9_\-]+(?<!\.atom)/, :group_id=>/[a-zA-Z.0-9_\-]+(?<!\.atom)/}
```

In this case, id is actually the title of the milestone, which can be anything at the moment.

After:

```
group_milestone  GET /groups/:group_id/milestones/:id(.:format)  groups/milestones#show {:id=>/[^\/]+/, :group_id=>/[a-zA-Z.0-9_\-]+(?<!\.atom)/}
```

2. `parameterize` would strip all Unicode characters, leaving a blank string. Rails would report something like:

ActionView::Template::Error (No route matches {:action=>"show", :controller=>"groups/milestones", :group_id=>#<Group id: 48, name: "ops-dev", path: "ops-dev", owner_id: nil, created_at: "2015-11-15 08:55:30", updated_at: "2015-12-02 06:23:26", type: "Group", description: "", avatar: "sha1.c71e73d51af1865c1bbbf6208e10044d46c9bb93.png", public: false>, :id=>"", :title=>"肯定不是中文的问题"} missing required keys: [:id]):

This change uses the babosa library to create a better slug, which surprisingly
isn't actually used by the global milestone controllers. Instead, they use the
title passed as a query string for some reason.

Closes https://github.com/gitlabhq/gitlabhq/issues/9881

Fix constraints

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

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

1f11096c included new filters but made it hard to determine which dropdown did
what. This patch restores the original placeholders.

The percent_complete method returns a value of 100 when a
ZeroDivisionError occurs. That seems like a very strange default for an
error case, and results in a bug when a milestone has no corresponding
issues (new, empty milestones show 100% completion). This commit changes
the rescue value to 0, and subsequently fixes #1656, which reported this
problem.