Persist tmp snippet uploads at users

See merge request gitlab/gitlabhq!3138

Guests can know whether merge request template name exists or not

See merge request gitlab/gitlabhq!3117

Also release `u` from TOP_LEVEL_ROUTES

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

It persist temporary personal snippets under
user/:id namespaces temporarily while creating
a upload record to track it. If an user gets removed
while it's still a tmp upload, it also gets removed.
If the tmp upload is sent, the upload gets moved to
personal_snippets/:id as before. The upload record
also gets updated to the new model type as well.

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

Previously, if a user was a guest member of a private project, they
could access the merge request template as we were not checking
permission-levels of the user.

When a issue template is asked for, the user must have :read_issue for
the project; or :read_merge_request when a merge request template is
asked for.

We also now rescue_from FileNotFoundError and handle as 404. This is
because RepoTemplateFinder can raise a FileNotFoundError exception,
which Rails previously handled as a 500.

Handling these in a way that is consistent with
ActiveRecord::RecordNotFound exceptions, within controllers that
inherit from Projects::ApplicationController at least, and returning a
404.

https://gitlab.com/gitlab-org/gitlab-ce/issues/54943

Move some project routes under - scope

See merge request gitlab-org/gitlab-ce!28830

This sets up all the basics for importing Phabricator tasks into
GitLab issues.

To import all tasks from a Phabricator instance into GitLab, we'll
import all of them into a new project that will have its repository
disabled.

The import is hooked into a regular ProjectImport setup, but similar
to the GitHub parallel importer takes care of all the imports itself.

In this iteration, we're importing each page of tasks in a separate
sidekiq job.

The first thing we do when requesting a new page of tasks is schedule
the next page to be imported. But to avoid deadlocks, we only allow a
single job per worker type to run at the same time.

For now we're only importing basic Issue information, this should be
extended to richer information.

Affected project routes are:

* services
* boards
* releases
* forks
* group_links
* import
* avatar
* labels
* milestones

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