The check for continue_params&.key?(:to) in Projects::ImportsController
caused an exception in redirect_to if this key contained a nil value.

Since url_for won't add any params for an empty hash, we can just return
that in continue_params if params[:continue] isn't present, and simplify
the code in the controllers to check for the values we actually want to
use.

Enables frozen string for some vestigial files as
well as the following:

* app/controllers/projects/**/*.rb
* app/controllers/sherlock/**/*.rb
* app/controllers/snippets/**/*.rb
* app/controllers/users/**/*.rb

Partially addresses #47424.

This whitelists all existing offenses for the various CodeReuse cops, of
which most are triggered by the CodeReuse/ActiveRecord cop.

This ensures that we have more visibility in the number of SQL queries
that are executed in web requests. The current threshold is hardcoded to
100 as we will rarely (maybe once or twice) change it.

In production and development we use Sentry if enabled, in the test
environment we raise an error. This feature is also only enabled in
production/staging when running on GitLab.com as it's not very useful to
other users.

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.

Fixing the issue of visiting a project fork url giving 500 error when not signed in instead of being redirected to the sign in page. The main reason is ApplicationController skips authentication if the project exists. To fix the issue, forced the authentication in ForksController when current_user is nil.

Fixes
https://dev.gitlab.org/gitlab/gitlabhq/issues/2649
https://gitlab.com/gitlab-org/gitlab-ce/issues/13956

1. Fix double bottom border if pagination
2. Fix broken search on forks page
4. Remove duplicate js logic
4. Remove unused show all link
5. Remove duplicate “no project” message in different views

After this merge request you can easily render shared projects template
with all necessary html/js included to make searchable list with
pagination. All you need to provide is controller that returns
projects list with seach nad pagination and render html form with
project-filter-form id and text field with filter_projects name.

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

* Also refactor query to get projects accessible for current user.
  ProjectsFinder actually return public projects when no user is passed.

Use import_status to track async import status and give feedback to the user

Closes #2388
Closes #2400