Snippets empty state

What does this MR do?

Adds empty state to project, user and dashboard snippets.

EE port: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/1614

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Screenshots (if relevant)

Screen_Shot_2016-11-10_at_05.26.24Screen_Shot_2016-11-10_at_05.26.54Screen_Shot_2016-11-10_at_05.27.37Screen_Shot_2016-11-10_at_05.26.44

Does this MR meet the acceptance criteria?

What are the relevant issue numbers?

Closes #20847 (moved)