Add support for cross project references for labels
## Summary
Support for cross project references for labels.
## Rationale
1. Cross project label references are currently not supported in GitLab
1. `to_reference` method signature in `Label` model breaks the abstraction introduced in `Referable`.
`concerns/referable.rb: def to_reference(_from_project = nil)`
Signatures:
```
label.rb: def to_reference(format = :id)
commit_range.rb: def to_reference(from_project = nil)
commit.rb: def to_reference(from_project = nil)
external_issue.rb: def to_reference(_from_project = nil)
group.rb: def to_reference(_from_project = nil)
issue.rb: def to_reference(from_project = nil)
merge_request.rb: def to_reference(from_project = nil)
milestone.rb: def to_reference(from_project = nil)
project.rb: def to_reference(_from_project = nil)
snippet.rb: def to_reference(from_project = nil)
user.rb: def to_reference(_from_project = nil)
```
This MR suggests using `def to_reference(from_project = nil, format: :id)` which makes use of keyword arguments and preserves abstract interface.
1. We need support for cross project label references when we want to move issue to another project
It may happen that issue description, system notes or comments contain reference to label and this reference will be invalid after moving issue to another project and will not be displayed correctly unless we have support for cross project references.
Merge request that needs this feature: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/2831
I think that cross project label references may be useful, (example: `Hey, see our issues for CI in GitLab CE! - gitab-org/gitlab-ce~"CI"`).
cc @JobV @DouweM @rspeicher
See merge request !2966
Add a spec for WikiPipeline
Removes the specs from GollumTagsFilter that were more like integration
tests for the pipeline than unit tests of the filter.
See merge request !3054
When `object_class.link_reference_pattern` was `nil` because object
being processed do not implemement link references `call` method
returned `nil` instead of returning document, even if document has been
processed in for basic reference pattern.
Update Gemojione for new hotness ✨
Before | After
------ | -----
 | 
See merge request !2800
- Apply the RelativeLinkFilter filter to other formats, e.g.,
reStructuredText so links from the Files view or the Project view work
- Remove the AsciidocPipeline pipeline
Fixes#3533.
Define a limited set of filters for SingleLinePipeline
Removes the following filters from its parent GfmPipeline:
- SyntaxHighlightFilter
- UploadLinkFilter
- TableOfContentsFilter
- LabelReferenceFilter
- TaskListFilter
Closes#1697
See merge request !2257
Removes the following filters from its parent GfmPipeline:
- SyntaxHighlightFilter
- UploadLinkFilter
- TableOfContentsFilter
- LabelReferenceFilter
- TaskListFilter
Closes#1697
Nokogiri produces inefficient XPath expressions when given CSS
expressions such as "a.gfm". Luckily these expressions can be optimized
quite easily while still achieving the same results.
In the two cases where this optimization is applied the run time has
been reduced from around 170 ms to around 15 ms.
Around 300 ms (in total) would be spent in these delegated methods due
to the extra stuff ActiveSupport adds to the compiled methods. Because
these delegations are so simple we can just manually define the methods,
saving around 275 milliseconds.