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