popover fixes, enhancements
popover fixes, enhancements

 * fix styling of .horizontal.top popovers (offset was wrong, only shadow
   was top-aligned)
 * add support for .horizontal.content-top, i.e. a popover whose arrow is
   just below the popover-title

Change-Id: I6b7afc75496d947698dc23152879842806e3abc1
Reviewed-on: https://gerrit.instructure.com/21233
Reviewed-by: Ryan Florence <2d8900489f91ac272fd9ce9d5789db6522668ca2@instructure.com>
Tested-by: Jenkins <d95b56ce41a2e1ac4cecdd398defd7414407cc08@instructure.com>
Product-Review: Jon Jensen <44f878afe53efc66b76772bd845eb65944ed8232@instructure.com>
QA-Review: Jon Jensen <44f878afe53efc66b76772bd845eb65944ed8232@instructure.com>

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