Attempting to use the /projects/:id API by specifying :id in
"namespace/project" format would always result in a 404 if the namespace
contained a dot.

The reason? From http://guides.rubyonrails.org/routing.html#specifying-constraints:

"By default the :id parameter doesn't accept dots - this is because the dot is
used as a separator for formatted routes. If you need to use a dot within an
:id add a constraint which overrides this - for example id: /[^\/]+/ allows
anything except a slash."

Closes https://github.com/gitlabhq/gitlabhq/issues/9573

Needed to support Huboard

Automatically fork a project when not allowed to edit a file.

Fixes #3215.

To do:

- [ ] Add tests

-----

## "Edit" button on file in a project the user does NOT have write access to

![edit_file](/uploads/7602157420768aef483a6586bba2d164/edit_file.png)

## Clicking will automatically create a fork

![during_fork](/uploads/32f4f5dff9f24ea99522000b0bf881c5/during_fork.png)

## When the fork has been created, the user is returned to the edit page on the original project with a notice

![edit_notice](/uploads/94ed1319404370ff1e9c0d672fb41e03/edit_notice.png)

## The user cannot change the target branch and is informed that editing will start an MR

![edit_footer](/uploads/4da68d4795c7177e575b7c434d16eeae/edit_footer.png)

## Hitting "Commit changes" will commit and start an MR from my fork to the origin project

![Screen_Shot_2015-12-17_at_23.38.08](/uploads/d777a4db6f38a5a1be84031694465bc1/Screen_Shot_2015-12-17_at_23.38.08.png)

-----

## "Create file, "Upload file" and "New directory" buttons in a project the user does NOT have write access to

![new_directory](/uploads/72f556248f30d6652523bbb4be01b3e0/new_directory.png)

## Clicking any of these options will automatically create a fork

![during_fork](/uploads/32f4f5dff9f24ea99522000b0bf881c5/during_fork.png)

## When the fork has been created, the user is returned to the tree page on the original project with a notice

![new_directory_notice](/uploads/a1a3e11308ae0e8f0913fae6813a37ed/new_directory_notice.png)

## Clicking "New directory" again will show the modal. The user cannot change the target branch and is informed that editing will start an MR

![new_dir](/uploads/99ca8cbfb2f70603e352b3fdf67b6281/new_dir.png)

## Hitting "Create directory" will commit and start an MR from my fork to the origin project

![Screen_Shot_2015-12-17_at_23.39.19](/uploads/3713d0235abf831361b803a6198c5bc1/Screen_Shot_2015-12-17_at_23.39.19.png)

cc @dzaporozhets @skyruler

See merge request !2145

This standardizes all the project API formats. Also needed to support Huboard.