Merge branches 'feature/project-export-ui-experimental' and 'feature/project-import' of gitlab.com:gitlab-org/gitlab-ce into feature/project-export-ui-experimental

Merge branches 'feature/project-export-ui-experimental' and 'feature/project-import' of gitlab.com:gitlab-org/gitlab-ce into feature/project-export-ui-experimental

Merge branches 'feature/project-export' and 'feature/project-import' of gitlab.com:gitlab-org/gitlab-ce into feature/project-import

Merge branch 'feature/project-import' of gitlab.com:gitlab-org/gitlab-ce into feature/project-export-ui-experimental

Merge branches 'feature/project-export-ui-experimental' and 'feature/project-import' of gitlab.com:gitlab-org/gitlab-ce into feature/project-export-ui-experimental

Merge branches 'feature/project-export-ui-experimental' and 'feature/project-import' of gitlab.com:gitlab-org/gitlab-ce into feature/project-export-ui-experimental

# Conflicts:
#	Gemfile.lock
#	app/helpers/todos_helper.rb
#	app/models/todo.rb
#	app/views/projects/edit.html.haml
#	lib/gitlab/import_export/import_service.rb

Merge branches 'feature/project-export' and 'feature/project-import' of gitlab.com:gitlab-org/gitlab-ce into feature/project-import

Merge branches 'feature/project-export' and 'feature/project-import' of gitlab.com:gitlab-org/gitlab-ce into feature/project-import

# Conflicts:
#	app/models/project.rb
#	db/schema.rb
#	lib/gitlab/import_export/import_export_reader.rb

Merge branches 'feature/project-export' and 'master' of gitlab.com:gitlab-org/gitlab-ce into feature/project-export

Improve SVG sanitizer to handle namespaced attributes

* Small refactor in the SVG sanitizer
* Enable already whitelisted namespaced attributes to be allowed
* Disable `xlink:href`to reference any external resource

Fixes #18100 

See merge request !4427

Fix Error 500 when using closes_issues API with an external issue tracker

Closes #18484

See merge request !4608

Closes #18484

Improvements to offscreen navigation

Improvements on top of https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4579 based on mockups from https://gitlab.com/gitlab-org/gitlab-ce/issues/18417#note_12389766

See merge request !4607

Resolve "Hide Left sidebar paradigm"

## What does this MR do?
Hides the nav bar by default & centers the tanuki logo in the top nav

## Why was this MR needed?
UX

## What are the relevant issue numbers?
Closes #18417 

## Screenshots (if relevant)
![Screen_Shot_2016-06-10_at_12.49.10_PM](/uploads/c281e4c9de1c1bc9af59ebfa8d2bd18b/Screen_Shot_2016-06-10_at_12.49.10_PM.png)
![Screen_Shot_2016-06-10_at_12.49.27_PM](/uploads/635e0a88230105faa5527f6632899ddb/Screen_Shot_2016-06-10_at_12.49.27_PM.png)
<img src="/uploads/3001a9c723037012f1b86cfacfb1225e/Screen_Shot_2016-06-10_at_12.51.41_PM.png" width="500px">

See merge request !4579