Fix cross-project label ref used with invalid project

When cross-project label reference was used with invalid project reference, `nil` was assigned to project variable which later caused an exception.

Closes #15168

See merge request !3811

add tap coverage example to project settings

Previously, there were examples for Simplecov, pytest-cov, and phpunit.
This adds an example for using the tap cli tool
(https://github.com/tapjs/node-tap)

Before:
![Screen_Shot_2016-04-07_at_9.57.32_AM](/uploads/2864d4cd4b5288565057263a435a851f/Screen_Shot_2016-04-07_at_9.57.32_AM.png)

After:

![Screen_Shot_2016-04-07_at_9.57.16_AM](/uploads/62901e01c4ad6db86e4ced3dfebd20b9/Screen_Shot_2016-04-07_at_9.57.16_AM.png)


See merge request !3597

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

Closes #15168

Disable spellcheck and autocorrect for username field in admin page

closes #14855

## before
![Screen_Shot_2016-04-19_at_9.25.12_AM](/uploads/19387c4a11a879e9034a2179e932436e/Screen_Shot_2016-04-19_at_9.25.12_AM.png)

## after
![Screen_Shot_2016-04-19_at_9.25.47_AM](/uploads/60f4eba6a97201333dc64e46d625aac2/Screen_Shot_2016-04-19_at_9.25.47_AM.png)

See merge request !3730

Refresh page according remaining todos

Fixes #14678 

See merge request !3428

Fix setting of "action" for Grape transactions

After wondering why we're not getting all the data in Grafana that I
wanted I realized I wasn't setting the "action" field properly here.

See merge request !3842

Wrap all code in diffs

Closes #15382  
Closes #15422  
All diff code wraps to next line instead of scrolling

<img src="/uploads/ec5754919bac0b027fcb122bb88435b3/Screen_Shot_2016-04-20_at_12.22.27_PM.png" width="500px">

See merge request !3838

[ci skip]

Add due date to issues

Closes: #12709

See merge request !3614

Merely setting the "action" tag will only result in the transaction
itself containing a value for this tag. To ensure other metrics also
contain this tag we must set the action using Transaction#action=
instead.

Articles on proper commit messages

2 Articles on commit messages

[ci skip]

See merge request !3831

Add Sentry logging for JavaScript errors

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/12675

See merge request !3795

Signed-off-by: Rémy Coutable <remy@rymai.me>

Signed-off-by: Rémy Coutable <remy@rymai.me>

Signed-off-by: Rémy Coutable <remy@rymai.me>

Signed-off-by: Rémy Coutable <remy@rymai.me>

Signed-off-by: Rémy Coutable <remy@rymai.me>

Fixed issue with dropdown not being toggleable again

Fix typos on sorting dropdown related to due date
Remove constant array and add Structs on Issue to keep due date data to fill options

Add due_date text field to sidebar issue#show
Add ability sorting issues by due date ASC and DESC
Add ability to filtering issues by No Due Date, Any Due Date, Due to tomorrow, Due in this week options
Add handling issue due_date field for MergeRequest
Update CHANGELOG
Fix ambigous match for issues#show sidebar
Fix SCREAMING_SNAKE_CASE offenses for due date contants
Add specs for due date sorting and filtering on issues

Increased z-index of right sidebar

Fixes issue with active button overlapping it

Closes #15243

See merge request !3722