Enables frozen string for the following:

* app/controllers/dashboard/**/*.rb
* app/controllers/explore/**/*.rb
* app/controllers/google_api/**/*.rb
* app/controllers/groups/**/*.rb
* app/controllers/import/**/*.rb
* app/controllers/instance_statistics/**/*.rb
* app/controllers/ldap/**/*.rb
* app/controllers/oauth/**/*.rb
* app/controllers/profiles/**/*.rb

Partially addresses #47424.

This commits replaces `params` with `safe_params` in `url_for` helpers
to resolve security issues [1] and failing specs with the

```
ArgumentError:
  Attempting to generate a URL from non-sanitized request parameters!
  An attacker can inject malicious data into the generated URL, such as
  changing the host. Whitelist and sanitize passed parameters to be secure.
```

error.

[1]: https://gitlab.com/gitlab-org/gitlab-ce/issues/45168

Previously, these wouldn't count issues or MRs in subgroups - meaning that if
_this_ group had no issues or MRs, we'd show the empty state, which was wrong.

In order to avoid string manipulation or modify route params (to make them unambiguous for `url_for`), we are accepting a behavior change:

When being redirected to the canonical path for a group, if you requested a group show path starting with `/groups/…` then you’ll now be redirected to the group at root `/…`.

Note: This changes the behavior of user lookups (see the spec change) so it acts the same way as groups and projects. Unauthenticated clients attempting to access a user page will be redirected to login whether the user exists and is publicly restricted, or does not exist at all.

Extended ProjectFinder in order to handle the following options:
 - current_user - which user use
 - project_ids_relation: int[] - project ids to use
 - params:
   -  trending: boolean
   -  non_public: boolean
   -  starred: boolean
   -  sort: string
   -  visibility_level: int
   -  tags: string[]
   -  personal: boolean
   -  search: string
   -  non_archived: boolean

GroupProjectsFinder now inherits from ProjectsFinder.
Changed the code in order to use the new available options.

* add parent_id field to namespaces table to store relation with nested groups
* create routes table to keep information about full path of every group and project
* project/group lookup by full path from routes table

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

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