Cleaner UI for login and signup pages

![Screenshot 2014-08-15 17.51.52](https://dev.gitlab.org/uploads/dzaporozhets/gitlabhq/fc8bf3c4a4/Screenshot_2014-08-15_17.51.52.png)
![Screenshot 2014-08-15 17.52.39](https://dev.gitlab.org/uploads/dzaporozhets/gitlabhq/72706f55b0/Screenshot_2014-08-15_17.52.39.png)
![Screenshot 2014-08-15 17.51.33](https://dev.gitlab.org/uploads/dzaporozhets/gitlabhq/c46f972944/Screenshot_2014-08-15_17.51.33.png)

See merge request !1022

Unify Nginx files to match as closely as possible

clarify which configs should be updated

remove prerelease note from 6.0 to 7.2 guide

[Documentation] cleanup installation guide formatting

make configuration comment spacing consistent

[Documentation] GitLab 7.2 requires GitLab shell 1.9.7

* Fix some formatting issues
* Make capitalization of titles consistent
* Update image that shows how to select branch

Fix installation version, we have 7.2 now

Change the branch name of cloning source to 7.2!! This also needs to be cherry picked to 7.2 stable branch

/cc @JobV @jacobvosmaer @marin

ps: unfortunately, there is mo 🤘 gemoji :(

See merge request !174

Protect unsubscribe path

See merge request !1033

Backticks cause quote

See merge request !704

Swap is required on servers with 1GB RAM

See merge request !1032

Bump required gitlab-shell version to 1.9.7

See merge request !1031

Add installing cmake to 7.2 update docs

See merge request !1029

Add dependency info for mysql-postgresql converter

upgrade ruby and gitlab shell config during 6.0->7.1 & 6.0->7.2 upgrades

Explain label migration

See merge request !1025

Update changelog

Fixes #1509

See merge request !1026

cmake is required during the installation of the rugged gem

Running converter with Python 2.6.x installed gives the following error:
AttributeError: 'module' object has no attribute 'check_output'

After installing Python 2.7.x everything works fine.

Fix spelling error in merge request performance issue warning.