add ?debug_js=1 for debugging only js; refs #8620
add ?debug_js=1 for debugging only js; refs #8620

?debug_assets=1 would give you unpackaged js and css (it's hardcoded into
jammit), which can be useful. However, we have a lot of stylesheets, and in IE,
sometimes we bump up against a limit when they aren't packaged. This makes it
difficult to debug javascript in IE, which is where ?debug_js=1 comes into play

test plan:
- in an environtment that has USE_OPTIMIZED_JS
- load any page with ?debug_js=1 on the end of the url
- make sure that you have a /assets/common.css bundle, but all the scripts
  still load separately

Change-Id: Id0daf4503c87ca9d74a36f19c17919e3647ed08a
Reviewed-on: https://gerrit.instructure.com/10943
Tested-by: Jenkins <d95b56ce41a2e1ac4cecdd398defd7414407cc08@instructure.com>
Reviewed-by: Ryan Florence <2d8900489f91ac272fd9ce9d5789db6522668ca2@instructure.com>

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