Add rake task to install or upgrade gitlab-shell installation.
Add documentation for new rake task to install gitlab-shell.
Editing preview
Multiple grammar/typo fixes in web hooks help
Add scoping to ldap lookup when only dn given
 Merge branch 'fix-grammar-help-webhooks' into 'master'

Fix grammar and typos in Webhooks help

This MR gets rid of some typos and wrong grammar in [help/web_hooks](https://gitlab.com/help/web_hooks).
Add uniq db index on project_id+iid
Add iids changelog entry
Migrate invalid rows with missing iids or duplicates
Add rake setup alias for gitlab:setup
Add doc file for dev rake tasks
Merge branch 'index_on_iid' into 'master'

 Add uniq db index on project_id+iid

Because:
* its faster
* it solves problem with repeating iid's in one project
Merge branch 'rake_setup' into 'master'

rake setup

Add alias `rake setup` to `rake gitlab:setup`
Mention in developer docs
Merge branch 'master' of https://github.com/gitlabhq/gitlabhq
Merge branch 'master' of https://gitlab.com/gitlab-org/gitlab-ce
Merge pull request #6857 from bytheway/master

Add scoping to ldap lookup when only dn given
Fix typo: Confiure -> Configure
Replace 6.0-to-6.7.md with 6.0-to-6.8.md
Use gitlab-shell 1.9.3
Merge pull request #6868 from cppcho/Confiure

Fix typo: Confiure -> Configure