fixes margin and padding

See merge request !2439
Update mailroom/postfix documentation [ci skip]
I worked with a customer to troubleshoot some strange Postfix and Mailroom issues. These doc updates aim to help other users avoid the same confusion.
See merge request !2430
Add pagination headers to already paginated API resources
Following #3045, I've added pagination headers using already available Kaminari methods.
## Pagination headers in action

---
I've also added a shared example to test paginated API resources.
A possible next step would be to paginate all the API resources that return an array.
See merge request !2426
Import GitHub wiki into GitLab
Closes#2834
GitHub doesn’t apply any constraints to theirs wiki slug allowing chars like ,, :, *, etc, we need to remove our constraints or some wiki pages will not be available after they are imported.
Some wikis use the Gollum's tags to link its internal/external resources like: images, urls, wiki pages, etc. So, to avoid that wiki links/images displays completely broken after they were imported, we added a new `WikiPipeline`, that for now will parse only simple links, and image tags.
##### Before `WikiPipeline`:

##### After `WikiPipeline`:

See merge request !2324
Unsubscribe from thread through link in email footer
Closes#3437


See merge request !2068
Since GitHub doesn’t apply these constraints to theirs wiki slug
allowing characters like `,`, `:`, `*`, etc, we need to relax our
constraints or some wiki pages will not be available after they were
imported.
For an example the Devise project have a wiki page with the following
slug: “How To: Add sign_in, sign_out, and sign_up links to your layout
template”
* master: (51 commits)
Fix version
Fix specs and rubocop warnings
Improve the consistency of commit titles, branch names, tag names, issue/MR titles, on their respective project pages
fixed LDAP activation on login to use new ldap_blocked state
Fix Admin/Users view to position buttons without spacing magic
Update to Go 1.5.3
Fix the undefinded variable error in Project's safe_import_url method
Update CHANGELOG [ci skip]
Add some cosmetic changes to variables API documentation [ci skip]
Fix misaligned edit button in milestone collection partial
Update button styles for Milestones#show
Modify builds API documentation style [ci skip]
Modify :ci_variable factory
Ensure the API doesn't return notes that the current user shouldn't see
Add 'Build' prefix to Variables entry name in API docs index
Fix some typos
Add spec for Note#cross_reference_not_visible_for?
Remove (invalid) timestamp formatting
Move `BroadcastMessage#status` to a helper since it's presentational
Update CHANGELOG
...
Conflicts:
doc/api/README.md
lib/api/api.rb
lib/api/entities.rb