adjust LTI external button to be aligned to the left and have spacing between text and its rendering

asadiqbal08: Updated branch as per suggestions
asadiqbal08: Addressed PR feedback
mattdrayer: Rebased branch, addressed merge conflict

Use django.utils.timezone.now() when determining if the due date of a component has passed to avoid tz-aware/naive datetime comparison bug

Toggle aria-hidden attribute on modal window open/close; Set title attribute on iframe to display name of component; Remove aria-labelledby attribute from modal body; Make modal overlay id attribute unique'