Closes #2104

Closes #1751

Closes #1592

Closes https://github.com/gitlabhq/gitlabhq/issues/9399

**What does this do?**
It adds validation to the creation of a wiki page, that way the user gets real
feedback instead of just a 404 page if the name of the wiki page was invalid

**Why is this needed?**
There are a lot of characters that are not allowed in the creation of a wiki
page, there is even a small text that is saying: Please don't use spaces.
Although we have that text there, we don't actually validate on this. This
commit adds validation on the title and gives the user actual feedback.

**What issues does this fix?**
Fixes http://github.com/gitlabhq/gitlabhq/issues/5357
Fixes https://github.com/gitlabhq/gitlabhq/issues/8565
Fixes https://github.com/gitlabhq/gitlabhq/issues/3913
Fixes https://github.com/gitlabhq/gitlabhq/issues/8166



Signed-off-by: Jeroen van Baarsen <jeroenvanbaarsen@gmail.com>

Closes #1547

Closes #1363

Make the following changes to deal with new behavior in Rails 4.1.2:

* Use nested resources to avoid slashes in arguments to path helpers.

The title format for wiki page may be unintelligible.
For example 'GitLab' is converted to 'Git Lab', 'MySQL' is converted to
'My Sql', etc.

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

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

The Cancel button on the Edit Wiki page was still redirecting back
to the "Index" page which is no longer the default Wiki page.

This commit changes the Cancel button in the following ways:

  * Pressing Cancel while editing an existing Wiki page will now
    redirect you back to the latest version of that page.
  * Pressing Cancel while editing a brand new Wiki home page that
    does not yet exist will redirect you to back to the same Edit
    Wiki Home page.

The previously failing Spinach steps have been fixed with this commit.
I have also added new steps that cover the entire usage of the Wiki
system.

The new Spinach steps revealed a minor bug in the Delete page process.
The path for the "Delete this page" button was previously set to
`project_wikis_page(@Project, @wiki)` when it should have been
using the singular `project_wiki_page(@Project, @wiki)` path helper.

The link has been corrected and all steps are now passing.