This reverts commit 2536fea8db0967a817615eb3e951eb6ba22f8ede.

An MR can only be resolved in the UI if:
- It has conflicts.
- It has valid diff_refs (in other words, it supports new diff notes).
- It has no conflicts with one side missing.
- It has no conflicts in binary files.
- It has no conflicts in files too large to display.
- It has no conflicts containing invalid conflict markers.

This change simplifies a Pipeline processing by introducing a special new status: created.
This status is used for all builds that are created for a pipeline.
We are then processing next stages and queueing some of the builds (created -> pending) or skipping them (created -> skipped).
This makes it possible to simplify and solve a few ordering problems with how previously builds were scheduled.
This also allows us to visualise a full pipeline (with created builds).

This also removes an after_touch used for updating a pipeline state parameters.
Right now in various places we explicitly call a reload_status! on pipeline to force it to be updated and saved.

So we have raw_diffs too

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

Instead calling diff_collection.count use diff_collection.size which is cache on the diff_collection

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

Speedup DiffNote#active? on discussions, preloading noteables and avoid touching git repository to return diff_refs when possible

- Preloading noteable we share the same noteable instance when more than one 
discussion refers to the same noteable.
- Any other call to that object that is cached in that object will be for any 
discussion.
- In those cases where merge_request_diff has all the sha stored to build a diff_refs get that 
diff_refs using directly those sha instead accessing to the git repository to first get the 
commits and later the sha.

Provide more sensible default sort order for issues and merge requests
based on the following table:

| type           | state  | default sort order |
|----------------|--------|--------------------|
| issues         | open   | last created       |
| issues         | closed | last updated       |
| issues         | all    | last created       |
| merge requests | open   | last created       |
| merge requests | merged | last updated       |
| merge requests | closed | last updated       |
| merge requests | all    | last created       |

NotesHelper#note_editable? and ProjectTeam#human_max_access currently
take about 16% of the load time of an issue page. This MR preloads
the maximum access level of users for all notes in issues and merge
requests with several queries instead of one per user and caches
the result in RequestStore.

This reverts commit c3935699.

1. Move render method to a concern, not a helper.
2. Let DiffHelper#diff_options automatically add the path option.
3. Move more instance var definitions to before filters.

When rendering a list of diff files, skip those where the diff is over
10 KB and provide an endpoint to render individually instead.

We just need to get merge requests closes issues when 
we’re going to show them