fix tool autoresize to account for canvas footer
fix tool autoresize to account for canvas footer

test plan:
 - load a page with an external tool
 - upon load, the tool should resize to fill most of the window
 - upon resize, the tool should resize to fill the new window size
   - the first resize should not cause the tool's size to "jump"

Change-Id: I59a7d2ab54f8d2e849b38908d59a91b1be09e8cc
Reviewed-on: https://gerrit.instructure.com/43147
Tested-by: Jenkins <d95b56ce41a2e1ac4cecdd398defd7414407cc08@instructure.com>
Reviewed-by: Nathan Mills <10b0771d20c18ad0d98c1d000665e443052b40b0@instructure.com>
QA-Review: August Thornton <9adc7a1161ddf32ff608de792a7e50179545f026@instructure.com>
Product-Review: Mark Severson <cdf1f90aee9d0d073a2a24141ebc71887f3ba533@instructure.com>

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