fixes #3115 and adds support for gif bmp & tiff images

when showing image preview check via lowercased extension and adds support for gif bmp & tiff images

Fix bubble padding.

Config setting should be used in git version check.

fix #3823

Save backup time as is.  Fixes #3857.

Fixed puma.rb environment setting

A small update of nginx example config to prevent users from issues while nginx not listen on localhost

Show only selected branch

A little change on wording for new-user email

included more details on searching for issues related to pull request

@options enable to keep params when switching ref.

Fixed a nginx configuration

update links to be relative paths and add CONTRIBUTING.md link

fixed fact about memory usage

fixed capitalization and added Google Analytics

Configure git global settings in installation docs

System calls to gitlab-shell were using unsanitized user input