Whenever we already deal with a User object, let's use the more specific
method avatar_icon_for_user.

fix issue #39843 Incorrect guidance stating blocked users will be removed from groups and projects as members

+ Add a partial for displaying user deletion guidance

- Add a `destroy_user` ability. This didn't exist before, and was implicit in
  other abilities (only admins could access the admin area, so only they could
  destroy all users; a user can only access their own account page, and so can
  destroy only themselves).

- Grant this ability to admins, and when the current user is trying to destroy
  themselves. Disallow destroying ghost users in all cases.

- Modify the `Users::DestroyService` to check this ability. Also check it in
  views to decide whether or not to show the "Delete User" button.

- Add a short summary of the Ghost User to the bio.

The user has the rights of a public user execpt it can never create a project,
 group, or team. Also it cant view internal projects.

This would help admins figure out from where spam is originating.

Closes #5908

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

This removes the need for running an extra SQL query in these cases.

Closes #2116
Closes https://github.com/gitlabhq/gitlabhq/issues/9502

Closes https://github.com/gitlabhq/gitlabhq/issues/9381

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

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

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

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

To prevent loose of group data you need to transfer or remove group
first before you can remove user

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

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.

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

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

add current sign-in date to admin section profile view