Added subnav to blame show, blob edit, builds show, commit builds, commit show, environments edit and pipelines show

Added subnav to new enviro view

Added sidebar top position calculation logic

Added sidebar translation to follow the subnav up when the body is scrolled until a certain limit

This object will manage Gitlab::Git::Compare instances

Introducing the concept of SafeDiffs which relates 
diffs with UI highlighting.

With new navigation design it makes no sense to duplicate title in the
header

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

Ci::Commit becomes a Pipeline object

1. Ci::Commit receives context: ref, :tag.
1. One Ci::Commit describes a one Pipeline
1. Pipeline is created from `.gitlab-ci.yml`
1. Pipeline is a ordered group of builds
1. We test MR against Pipeline
1. Pipelines have a separate view (https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/3703)
1. Pipeline can be triggered from UI (https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/3703)
1. Later we change `Trigger -> TriggerRequest -> Build` to `Trigger -> Pipeline` (future)
1. We add a Pipeline Hook that will be triggered on Pipeline status change  (future)
1. We extend notifications to use `Pipeline Hook` to send summary on pipeline changes (future)

After merging that I'll prepare a separate MR that will unify naming, database columns, table names:
```
Ci::Commit -> Pipeline
Ci::Build -> Build
CommitStatus -> Job
GenericCommitStatus -> ExternalJob

ci_commits -> pipelines
ci_builds -> jobs
```

This MR implements first 5 points.

This is made to solve this issue https://gitlab.com/gitlab-org/gitlab-ce/issues/14149.

See merge request !3653

Issue: https://gitlab.com/gitlab-org/gitlab-ce/issues/12785
Merge Request: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/3514