Make all pages in canvas full-width
Make all pages in canvas full-width

closes LS-1745
flag=none

test plan:
  - turn the new_user_tutorial flag off
  - pick a page, any page
  - make your browser wider than 1459px or so
  > expect the content to stretch the full width of the window
    (I know this used to be limited when editing a wiki page)

Change-Id: Iab76d2eef1762910150442c486f08cc01a709903
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/256894
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Jackson Howe <318c10a818c1b1f2ec50cdcb1827b2c6c5ebd7dc@instructure.com>
QA-Review: Jackson Howe <318c10a818c1b1f2ec50cdcb1827b2c6c5ebd7dc@instructure.com>
Product-Review: Peyton Craighill <b6cfaee6364b0ff4306081e7e83cf8ccde7c2fba@instructure.com>

instructure/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms