Refactor, simplify and unify helpers for rendering markup

Improve AsciiDoc rendering

See https://github.com/gitlabhq/gitlabhq/pull/9288

How to dump a production DB to staging

See merge request !1825

Fix labels for project/snippet visibility selection

Closes #1626

See merge request !671

Fix default tooltip placement

Made a logic error in 1e1785cc that prevented elements with the `has_tooltip` class from having the default tooltip placement if they didn't define one.

See merge request !674

Explain reset token expiration in emails

Update the new user emails to tell new users when their password reset token expires and provide a link to get a new one.  See #1921.  This MR adds new text to the emails:

```html
This link is valid for X days.  After it expires, you can <a href='new_user_password_url'>request a new one</a>
```

It will be more difficult to add the same link to the error message that's displayed when a user tries to reset his password with an expired token.  Currently, we don't know why the password change fails, we just show the Devise error messages on the form.

See merge request !1803

Add search issues/MR by number

It allows user to search issues/MR by number, e.g. `#3`.

Solves this [request](http://feedback.gitlab.com/forums/176466-general/suggestions/4235923-search-issues-by-number).

See merge request !668

Make more migrations reversible

See merge request !646

Now they line up with their title.

Don't display the password editing form if the user's token is expired;
redirect to the form that allows users to request a new password reset
token.

Tell new users when their password reset token expires and provide a
link to get a new one.

Don't send notifications to mentioned users that don't have access to the project in question.

Fixes internal issue https://dev.gitlab.org/gitlab/gitlabhq/issues/2325.

See merge request !664

Set gitlab.rb in Docker single image to make PostgreSQL start up properly

See gitlab-org/omnibus-gitlab#552

See merge request !661

Don't require DB connection in AttrEncrypted.

See merge request !667

Ensure that the first added admin performs repository imports

Update installation/update guides for 7.11.

See merge request !665

Fix push event.

Fixes issue with !653.

See merge request !663