max width on avatar pics
max width on avatar pics

Avatar pictures had an explicit height, but
the width could be whatever. Setting the max-width
will help keep it horizontally bounded for
layout purposes.

test plan:
- pick an avatar image that is really wide
- go to a discussion where you have posted
- make sure the avatar picture is not wider than 50px

Change-Id: I1a3d26bf28f70cb6948010f096c8b940f0a0ca26
Reviewed-on: https://gerrit.instructure.com/9022
Tested-by: Hudson <dfb64870173313a9a7b56f814c8e3b33e268497a@instructure.com>
Reviewed-by: Ryan Shaw <ea3cd978650417470535f3a4725b6b5042a6ab59@instructure.com>

em2/canvas-lms,fronteerio/canvas-lms,venturehive/canvas-lms,tgroshon/canvas-lms,usmschuck/canvas,redconfetti/canvas-lms,djbender/canvas-lms,tgroshon/canvas-lms,Unow/canvas-lms,leftplusrightllc/canvas-lms,ankithbti/canvas_lms,roxolan/canvas-lms,sdeleon28/canvas-lms,whalejasmine/canvas-lms,landonwilkins/canvas-lms,utkarshx/canvas-lms,landonwilkins/canvas-lms,Jyaasa/canvas-lms,arrivu/arrivu-lms,matematikk-mooc/canvas-lms,sdeleon28/canvas-lms,jay3126/canvas-lms,kyroskoh/canvas-lms,roxolan/canvas-lms,parbros/red-innovadores-lms,HotChalk/canvas-lms,Unow/ins,arrivu/hoodemo,rup/Tarrax,SwinburneOnline/canvas-lms,va7map/canvas-lms,instructure/canvas-lms,wye0220/shindig-canvas,samuels410/greatlakes-lms,efrj/canvas-lms,dgynn/canvas-lms,efrj/canvas-lms,greyhwndz/canvas-lms,arrivu/hoodemo,parbros/red-innovadores-lms,va7map/canvas-lms,arrivu/arrivu-lms,greyhwndz/canvas-lms,ankithbti/canvas_lms,instructure/canvas-lms,skmezanul/canvas-lms,arrivu/qibla-ecampus,samuels410/greatlakes-lms,merichar/canvas-lms,greyhwndz/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,rup/Tarrax,shidao-fm/canvas-lms,eCNAP/CANVAS,Jyaasa/canvas-lms,sfu/canvas-lms,arrivu/jigsaw-lms,usmschuck/canvas,fronteerio/canvas-lms,juoni/canvas-lms,eCNAP/CANVAS,snehakachroo1/LSI_replica,leftplusrightllc/canvas-lms,utkarshx/canvas-lms,merichar/canvas-lms,narigone/canvas,snehakachroo1/LSI_replica,HotChalk/canvas-lms,instructure/canvas-lms,parbros/red-innovadores-lms,Unow/ins,va7map/canvas-lms,jay3126/canvas-lms,dgynn/canvas-lms,grahamb/canvas-lms,loganrun/pincan,ShreniiNepal/shrenii_lmp,nditech/red-innovadores-lms,icelab/canvas,utkarshx/canvas-lms,arrivu/jigsaw-lms,fronteerio/canvas-lms,skmezanul/canvas-lms,antoniuslin/canvas-lms,roxolan/canvas-lms,SwinburneOnline/canvas-lms,ShreniiNepal/shrenii_lmp,landonwilkins/canvas-lms,Unow/ins,efrj/canvas-lms,sli7246/canvas_branch,matematikk-mooc/canvas-lms,SwinburneOnline/canvas-lms,SwinburneOnline/canvas-lms,antoniuslin/canvas-lms,Jyaasa/canvas-lms,wrdsb/canvas-lms,gbleydon/canvas-lms,sdeleon28/canvas-lms,arrivu/hiring-site,sfu/canvas-lms,dgynn/canvas-lms,Jyaasa/canvas-lms,arrivu/hoodemo,shidao-fm/canvas-lms,samuels410/greatlakes-lms,roxolan/canvas-lms,gbleydon/canvas-lms,venturehive/canvas-lms,em2/canvas-lms,sfu/canvas-lms,AndranikMarkosyan/lms,loganrun/pincan,snehakachroo1/LSI_replica,arrivu/hiring-site,tgroshon/canvas-lms,tgroshon/canvas-lms,Rvor/canvas-lms,venturehive/canvas-lms,Unow/canvas-lms,grahamb/canvas-lms,em2/canvas-lms,Rvor/canvas-lms,kyroskoh/canvas-lms,greyhwndz/canvas-lms,grahamb/canvas-lms,efrj/canvas-lms,grahamb/canvas-lms,leftplusrightllc/canvas-lms,Unow/canvas-lms,gbleydon/canvas-lms,leftplusrightllc/canvas-lms,instructure/canvas-lms,whalejasmine/canvas-lms,skmezanul/canvas-lms,shidao-fm/canvas-lms,nditech/red-innovadores-lms,antoniuslin/canvas-lms,matematikk-mooc/canvas-lms,redconfetti/canvas-lms,grahamb/canvas-lms,skmezanul/canvas-lms,sli7246/canvas_branch,sli7246/canvas_branch,rup/Tarrax,jay3126/canvas-lms,fronteerio/canvas-lms,snehakachroo1/LSI_replica,icelab/canvas,arrivu/jigsaw-lms,wrdsb/canvas-lms,sfu/canvas-lms,arrivu/hiring-site,wrdsb/canvas-lms,wye0220/shindig-canvas,utkarshx/canvas-lms,arrivu/arrivu-lms,va7map/canvas-lms,juoni/canvas-lms,ankithbti/canvas_lms,wye0220/shindig-canvas,dgynn/canvas-lms,instructure/canvas-lms,HotChalk/canvas-lms,wimemx/Canvas,kyroskoh/canvas-lms,ShreniiNepal/shrenii_lmp,usmschuck/canvas,nditech/red-innovadores-lms,usmschuck/canvas,sfu/canvas-lms,whalejasmine/canvas-lms,wimemx/Canvas,nditech/red-innovadores-lms,juoni/canvas-lms,arrivu/qibla-ecampus,antoniuslin/canvas-lms,AndranikMarkosyan/lms,wimemx/Canvas,landonwilkins/canvas-lms,djbender/canvas-lms,djbender/canvas-lms,matematikk-mooc/canvas-lms,sdeleon28/canvas-lms,instructure/canvas-lms,merichar/canvas-lms,juoni/canvas-lms,narigone/canvas,icelab/canvas,shidao-fm/canvas-lms,jay3126/canvas-lms,djbender/canvas-lms,wrdsb/canvas-lms,kyroskoh/canvas-lms,HotChalk/canvas-lms,arrivu/qibla-ecampus,samuels410/greatlakes-lms,whalejasmine/canvas-lms,Rvor/canvas-lms,eCNAP/CANVAS,loganrun/pincan,narigone/canvas,redconfetti/canvas-lms,ShreniiNepal/shrenii_lmp,eCNAP/CANVAS,redconfetti/canvas-lms,sfu/canvas-lms,venturehive/canvas-lms,Rvor/canvas-lms,narigone/canvas,AndranikMarkosyan/lms,AndranikMarkosyan/lms