allow html5 fullscreen for the canvadocs iframe
allow html5 fullscreen for the canvadocs iframe

Adds the "allowfullscreen" attribute to the iframe created for Canvadoc
documents, signalling that Canvadocs can open into fullscreen.

fixes CNVS-13650

test plan:
 * configure canvadocs, and view a file with it
 * verify that the canvadocs iframe has "allowfullscreen" as an
   attribute

Change-Id: I84b8b01796caa7291246dca6050ccdf13cca3813
Reviewed-on: https://gerrit.instructure.com/36503
Reviewed-by: Simon Williams <088e16a1019277b15d58faf0541e11910eb756f6@instructure.com>
QA-Review: Amber Taniuchi <ef4bfd1e6d278f6bc7d4a478f02be2cb9581a0a5@instructure.com>
Tested-by: Jenkins <d95b56ce41a2e1ac4cecdd398defd7414407cc08@instructure.com>
Product-Review: Zach Wily <9de8c4480303b5335cd2a33eefe814615ba3612a@instructure.com>

Jyaasa/canvas-lms,kyroskoh/canvas-lms,grahamb/canvas-lms,efrj/canvas-lms,utkarshx/canvas-lms,HotChalk/canvas-lms,redconfetti/canvas-lms,kyroskoh/canvas-lms,matematikk-mooc/canvas-lms,juoni/canvas-lms,instructure/canvas-lms,gbleydon/canvas-lms,wrdsb/canvas-lms,djbender/canvas-lms,samuels410/greatlakes-lms,tgroshon/canvas-lms,Rvor/canvas-lms,shidao-fm/canvas-lms,eCNAP/CANVAS,redconfetti/canvas-lms,greyhwndz/canvas-lms,Rvor/canvas-lms,instructure/canvas-lms,matematikk-mooc/canvas-lms,snehakachroo1/LSI_replica,utkarshx/canvas-lms,kyroskoh/canvas-lms,AndranikMarkosyan/lms,grahamb/canvas-lms,sdeleon28/canvas-lms,Unow/canvas-lms,Unow/canvas-lms,whalejasmine/canvas-lms,juoni/canvas-lms,Rvor/canvas-lms,grahamb/canvas-lms,roxolan/canvas-lms,jay3126/canvas-lms,ShreniiNepal/shrenii_lmp,gbleydon/canvas-lms,matematikk-mooc/canvas-lms,redconfetti/canvas-lms,SwinburneOnline/canvas-lms,greyhwndz/canvas-lms,jay3126/canvas-lms,HotChalk/canvas-lms,efrj/canvas-lms,dgynn/canvas-lms,roxolan/canvas-lms,djbender/canvas-lms,instructure/canvas-lms,djbender/canvas-lms,SwinburneOnline/canvas-lms,samuels410/greatlakes-lms,eCNAP/CANVAS,sfu/canvas-lms,sfu/canvas-lms,antoniuslin/canvas-lms,sfu/canvas-lms,whalejasmine/canvas-lms,tgroshon/canvas-lms,narigone/canvas,whalejasmine/canvas-lms,utkarshx/canvas-lms,venturehive/canvas-lms,samuels410/greatlakes-lms,wrdsb/canvas-lms,AndranikMarkosyan/lms,wrdsb/canvas-lms,sfu/canvas-lms,skmezanul/canvas-lms,dgynn/canvas-lms,Jyaasa/canvas-lms,roxolan/canvas-lms,djbender/canvas-lms,HotChalk/canvas-lms,greyhwndz/canvas-lms,sfu/canvas-lms,leftplusrightllc/canvas-lms,juoni/canvas-lms,greyhwndz/canvas-lms,antoniuslin/canvas-lms,fronteerio/canvas-lms,instructure/canvas-lms,skmezanul/canvas-lms,Unow/canvas-lms,gbleydon/canvas-lms,instructure/canvas-lms,sdeleon28/canvas-lms,leftplusrightllc/canvas-lms,wrdsb/canvas-lms,Rvor/canvas-lms,antoniuslin/canvas-lms,eCNAP/CANVAS,redconfetti/canvas-lms,skmezanul/canvas-lms,efrj/canvas-lms,va7map/canvas-lms,fronteerio/canvas-lms,Jyaasa/canvas-lms,va7map/canvas-lms,SwinburneOnline/canvas-lms,shidao-fm/canvas-lms,narigone/canvas,HotChalk/canvas-lms,SwinburneOnline/canvas-lms,utkarshx/canvas-lms,eCNAP/CANVAS,juoni/canvas-lms,instructure/canvas-lms,leftplusrightllc/canvas-lms,tgroshon/canvas-lms,whalejasmine/canvas-lms,venturehive/canvas-lms,va7map/canvas-lms,AndranikMarkosyan/lms,fronteerio/canvas-lms,leftplusrightllc/canvas-lms,ShreniiNepal/shrenii_lmp,va7map/canvas-lms,skmezanul/canvas-lms,ShreniiNepal/shrenii_lmp,AndranikMarkosyan/lms,kyroskoh/canvas-lms,sdeleon28/canvas-lms,ShreniiNepal/shrenii_lmp,venturehive/canvas-lms,tgroshon/canvas-lms,grahamb/canvas-lms,fronteerio/canvas-lms,snehakachroo1/LSI_replica,venturehive/canvas-lms,snehakachroo1/LSI_replica,antoniuslin/canvas-lms,matematikk-mooc/canvas-lms,wye0220/shindig-canvas,samuels410/greatlakes-lms,dgynn/canvas-lms,instructure/canvas-lms,snehakachroo1/LSI_replica,roxolan/canvas-lms,grahamb/canvas-lms,narigone/canvas,shidao-fm/canvas-lms,dgynn/canvas-lms,sdeleon28/canvas-lms,sfu/canvas-lms,jay3126/canvas-lms,sfu/canvas-lms,efrj/canvas-lms,wye0220/shindig-canvas,wye0220/shindig-canvas,jay3126/canvas-lms,narigone/canvas,Jyaasa/canvas-lms,shidao-fm/canvas-lms