Update markdown reference to external issues

1. Issue may be not only in jira.
2. Rewrite method for support different external issue trackers
change bash to sh
fix bash-ism
Update markdown.rb

Fix mistake by @qqshfox report
fix link_to by @bwrsandman

Add missing '#'
add current sign-in date

add current sign-in date to admin section profile view
Mention that people should use the CentOS tools.
update ssl_ciphers

taken from
https://raymii.org/s/tutorials/Strong_SSL_Security_On_nginx.html /
https://cipherli.st/

backwards compatible ciphers not needed since gitlab does not support
ie8
simplify HTTPS setup details

also adds comment about updating nginx files during upgrades
add optional nginx configs to make more secure
Merge pull request #7596 from bbodenmiller/patch-5

add current sign-in date
Merge branch 'name-it-centos' into 'master'

Name it centos

See merge request !1060
Recommend the GitLab Development Kit
Use create-hooks instead of rewrite-hooks.sh

The rewrite-hooks.sh script is a deprecated wrapper for gitlab-shell's
create-hooks script.
add cleanup section to 5.0 upgrade guide

Add cleanup details to upgrade guide as gitolite and more is no longer
used
Merge pull request #7668 from bbodenmiller/patch-15

add cleanup section to 5.0 upgrade guide
Merge pull request #7580 from bbodenmiller/patch-7

add optional nginx configs to make more secure
Merge pull request #7583 from bbodenmiller/https

[Documentation] simplify HTTPS setup details
Merge branch 'master' of github.com:gitlabhq/gitlabhq
Merge branch 'create-hooks' into 'master'

Use create-hooks instead of rewrite-hooks.sh

The rewrite-hooks.sh script is a deprecated wrapper for gitlab-shell's
create-hooks script.

See merge request !1068