Monthly release document update

See merge request !1092

Conflicts:
	doc/install/installation.md

Revert sticky headers

See merge request !1104

This reverts commit 6eb85b1a.

Save last scrollposition and scroll back when leaving ZEN mode

improve 7.3 upgrade process & redis setup

update gitlab shell to 1.9.8 for gitlab 7.2.2

Typo it -> its.

formatting improvements to 6.0-to-7.3.md

Fixes
https://github.com/gitlabhq/gitlabhq/commit/2b35c887904b6a7a05a7c88fdf1ccd66ba943e20#commitcomment-7829537,
https://github.com/gitlabhq/gitlabhq/commit/5704e6fee9d2dea67c4a91b43d06a9958484d29b#commitcomment-7829367,
&
https://github.com/gitlabhq/gitlabhq/commit/5704e6fee9d2dea67c4a91b43d06a9958484d29b#commitcomment-7829381

As committed in https://github.com/gitlabhq/gitlabhq/commit/873acfd9aa54e801d5786c32b05c4f8ad21af72a GitLab 7.2.2 requires GitLab Shell 1.9.8. Fixes https://github.com/gitlabhq/gitlabhq/issues/7806.

Prevent default action when closing zen mode

Factor zen mode.

Adds support for ruby 1.8 in webhook example

By using the hash rocket syntax, the web hook will work on older versions of ruby (1.8) in addition to 1.9, 2.0 ect..
Moves do .. end to separate lines for ruby-lint.

Additional Information:
http://stackoverflow.com/questions/25899476/webrick-gives-error-unexpected-expecting-end
https://github.com/spuder/r10k_gitlab_webhook

Ignore tags file.

link to page that discusses how to generate ssh key

Improve zen mode internals.

Release branch earlier

Fixes #1603

See merge request !1102

Same version restore

Warn users about this.

See merge request !1101