Add feature specs for note polling

Ref. #4032, !2084

cc @rspeicher 

See merge request !2086

This also increases capybara timeout to 15 seconds (note polling
interval). Capybara will look for new note for this period of time.

Ref. #4032, !2084

Fix note polling

Closes #4032

See merge request !2084

Preserve trailing new lines at the end of file on the online editor

Fixes #3784

Because Haml automatically indents the HTML source code, the contents
of whitespace-sensitive tags like pre and textarea can get screwed up.

See merge request !2099

Clean up CONTRIBUTING.md

* Use 80 chars width where possible
* Remove easyfix label reference
* Add new issue submission template
* Add long links to the bottom of the page

See merge request !2100

* Use 80 chars width where possible
* Remove easyfix label reference
* Add new issue submission template
* Add long links to the bottom of the page

Because Haml automatically indents the HTML source code, the contents
of whitespace-sensitive tags like pre and textarea can get screwed up.

update guides for feature proposals on the issue tracker

see also #4038 

cc @sytses 

See merge request !2094

Fix Typo [mailinglist to mailing list]

Closes: #4078 

See merge request !2098

[ci skip]

Add upgrade guide for 8.2 to 8.3

Making sure we don't forget mentioning the need to upgrade Redis from
!1888. Added this in preparation for 8.3.

[ci skip]

See merge request !2085

[ci skip]

[ci skip]

[ci skip]

[ci skip]

Suppress warning about missing `.gitlab-ci.yml` if builds are disabled

When user disables GitLab Ci Service in project's settings then warning
about missing `.gitlab-ci.yml` file should be supressed. This a matter
of user experience as stated in #3761 (closes #3761).

cc @ayufan 

See merge request !2014

[ci skip]

Persist CI runners registration token

This MR adds feature of persisting CI runners registration token.
User will be able to generate and then reset (if necessary to revoke) this token.

This closes #3703 

cc @ayufan 

See merge request !2039

* master:
  Move CI admin builds and runners specs to correct directory
  Fix 500 when viewing specific runners on runners page
  Fix Ci::Project migration not migrating columns that cannot be NULL
  Fix MySQL migration of CI emails
  Minor fix in flow 'Merge when build succeeds'

Move CI admin builds and runners specs to correct directory [ci skip]

/cc @grzesiek 

See merge request !2095

Fix CI project migration and 500 on runners page



See merge request !2093