Unclear how to enable CI for the project

1. User creates project Foo
2. User goes to project Foo settings
3. User sees CI settings section like this and has no idea how enable CI

cc @skyruler @jschatz1 @ayufan @JobV

TODO

• Add links to CI documentation for 8.6+ (gitlab-ce!3384)
• Remove builds settings from Project settings (gitlab-ce#13697)
• We replace link to docs on Builds page with one that creates .gitlab-ci.yml file in web editor
• Add .gitlab-ci.yml templates for most popular languages as dropdown in web editor
• Based on repository language automatically suggest best template