add display_type configuration to external tools

this setting should allow tools to choose how they are displayed
in the canvas interface. the new full width display removes the
canvas sidebars, footer, and breadcrumbs.

test plan:
 - install a tool with course_navigation and account_navigation
   extensions.
 - make sure the tool displays normally without a display_type
   configuration.
 - use a console to set display_type = 'full_width' in a tool's
   course_navigation settings.
 - the tool should display as a "full width" tool when viewed
   by the course navigation link. full width means without the
   left or right side bar, without breadcrumbs, and without a
   footer. the canvas header should still be displayed.
 - the tool should display normally when viewed by the account
   navigation link.
 - use the console to set the display_type = 'full_width' in the
   tool's top level settings.
 - tool tool should now display full width using the account
   navigation link.

Change-Id: Idc19c0c96031bd80a45ce984241c23e4ce1efe78
Reviewed-on: https://gerrit.instructure.com/35160
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Brad Humphrey <brad@instructure.com>
QA-Review: August Thornton <august@instructure.com>
Product-Review: Jon Willesen <jonw@instructure.com>