fix alignment
allow session_id to be undefined when starting kernel channels
update font-awesome
genereate css
remove redundant 'responsive-utilities' from style.less

it's already included in bootstrap.less
Merge pull request #6691 from minrk/rm-bs

remove redundant 'responsive-utilities' from style.less
Merge pull request #6685 from minrk/allow-no-session-id

allow session_id to be undefined when starting kernel channels
Merge pull request #6669 from SylvainCorlay/font_awesome_update

Font awesome update
Merge pull request #6681 from SylvainCorlay/widget_hbox_align

Minor change in widgets.less to fix alignment issue