Add a page title to every page.

![You get a title, and you get a title; everyone gets a title!](https://i.imgflip.com/kvmq8.jpg)

The `page_title` helper pushes the provided string at the end of the title, but because of the order that layouts are rendered in by ActionView, the result is always this:

```
<title from view> |
<title from as specified in the controller or by its layout> |
<title from layouts/_head>
```

For example: `Merge Requests | GitLab.org / Gitlab Community Edition | GitLab`.

All a developer needs to know is to put a `page_title` call describing the page in question at the start of every template.

To get everything where I wanted it to go without too much duplication, I had to make some changes around layouts, sidebars and controllers.

See merge request !593

More HTML::Pipeline filters

The big part of this MR is a feature that is intended to test the entire Markdown-parsing process from beginning to end. See `spec/support/markdown_feature.rb` and `spec/features/markdown_spec.rb`.

One big thing this MR fixes is not being able to type a `<` or `>` anywhere. It now gets properly escaped.

This MR also adds three more custom HTML::Pipeline filters:

### AutolinkFilter

Similar to the built-in Autolink filter in that it still uses Rinku for standard http and ftp links, but then does some further processing to allow auto-linking of any URI scheme. See internal issue https://dev.gitlab.org/gitlab/gitlabhq/issues/2239

### SanitizationFilter

Created a simple custom SanitizationFilter that sub-classes the default one and adds our custom whitelisting.

### TableOfContentsFilter

Adds the anchor links to each header. This removes some processing from our Redcarpet renderer.

Closes #800, #1015, #1528, #1549

Closes GitHub [8535](https://github.com/gitlabhq/gitlabhq/issues/8535)

See merge request !584

Add link to services api doc.

Just a one-line change to link in the services api doc.

I'm curious though. Only gitlab-ci and hipchat are supported.  Would you accept a pull request for the other services? Actually I [submitted](http://feedback.gitlab.com/forums/176466-general/suggestions/7667256-add-api-calls-for-all-services-in-a-project) that last question to the feedback tool.

See merge request !544

While `escape_once` will create this HTML entity, Nokogiri always
translates it back before it gets to IssueReferenceFilter, so there
should be no danger of erroneous issue links.

This just extends the HTML::Pipeline::SanitizationFilter with our custom
whitelist.

Removes header and table of contents processing from Redcarpet renderer.

Update upgrader doc to point to 7.10.1.

See merge request !594

Fix DB error when trying to tag a repository

Steps to reproduce: Go to a project settings, add tags, click on save changes

Observed behavior: Error 500

```
    PG::Error: ERROR:  column "taggings_count" does not exist
        LINE 1: UPDATE "tags" SET "taggings_count" = COALESCE("taggings_coun...
```

Ran `rake acts_as_taggable_on_engine:install:migrations`, removed the first
migration that created the `tags` and `taggings` table, and added the rest.

* Closes #1512
* Closes #1550
* Closes https://github.com/gitlabhq/gitlabhq/issues/6867
* Closes https://github.com/gitlabhq/gitlabhq/issues/9194

See merge request !577