Update markdown reference to external issues

1. Issue may be not only in jira.
2. Rewrite method for support different external issue trackers
Delete mailer queue because we don't use sidekiq_mailer gem and now the mailer queue doesn't exist any more.
change bash to sh
fix bash-ism
set the collation to utf8_general_ci

I get problems with strange characters in merge requests unless the collation is set to utf8_general_ci

set the collation to utf8_general_ci

I get problems with strange characters in merge requests unless the collation is set to utf8_general_ci

set the collation to utf8_general_ci

I get problems with strange characters in merge requests unless the collation is set to utf8_general_ci
Remove unused title parameter.

It is always overridden by to humanized source branch name by
MergeRequests::BuilService, which is used by new_project_merge_request_path.
Fix not rendered the network graph edge.
Update user_management.md

add rails_env to commands
Update markdown.rb

Fix mistake by @qqshfox report
move env to end of lines
fix link_to by @bwrsandman

Add missing '#'
Document the extra.sign_in_text setting for CE
Update highlight.js to 8.2, fixes #519
add sign-in count

add sign-in count to admin section profile view
add current sign-in date

add current sign-in date to admin section profile view
Add article about GitLab flow.
Add GitLab Flow to the index.
Fix grammar mistakes, thanks Angus
Make tree readme title - a link with anchor to README section

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>
add missing config files to check during release process