Display nav controls on mobile

Set inputs inside .nav-controls to full-width on viewports below 600px

Fixes #13885 (closed)

Affected pages

/dashboard/groups

/admin/builds

/dashboard/projects

/dashboard/issues

/dashboard/merge_requests

/dashboard/milestones

/dashboard/todos

/explore

/groups/{group-name}/issues

/groups/{group-name}

/groups/{group-name}/milestones

/{group-name}/{project-name}/builds

/{group-name}/{project-name}/forks

/{group-name}/{project-name}/issues

/{group-name}/{project-name}/labels

/{group-name}/{project-name}/merge_requests

/{group-name}/{project-name}/milestones

/{group-name}/{project-name}/wikis/home

/{group-name}/{project-name}/wikis/pages

Some Screenshots

Groups

Admin > Builds

TODOs

Dashboard > Projects

Project Issues

Project Merge Requests