New settings added to enable or disable project features by default

Conflicts:
	config/gitlab.yml.example
	config/initializers/1_settings.rb
Default values for project features added to create context
Reducing database access.
Allow vertical scrolling on Network graph
Render graph partially.
Fixed typo in project hook documentation
Fix minor bug about line overlap.
Add test related to a bug of network graph.
Fix Gitlab::Git::Repository#commit returns wrong commit, if commit_id is "tag name".
Merge giggsey:patch-1 into improve-performance-of-network-graph
Draging network graph is replaced by vertical scrolling.
Merge pull request #3741 from hiroponz/improve-performance-of-network-graph

Improve performance of network graph
Merge pull request #3731 from coldfrontlabs/master

Fix typo in Project API documentation for deleting hooks
No unicorn config. Use higher version of gitlab-she;;
Wall and snippets were disabled by default
Merge pull request #3707 from Undev/default_project_settings

Default settings for project features
Change text_field to :login from :email in line with 9d92433a7c83432657faf4c02839bba1ba6f22ac to allow login as admin or non-ldap user when ldap is enabled
Also change haml style in line with that commit
Handle several RDBMS
Update memory requirements after puma.
Merge branch 'requirements-after-puma' of /home/git/repositories/gitlab/gitlabhq