Visual styling for LTI external button

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

PHX-256 Added a white background to the modal window close button

asadiqbal08/WL-356: Add I18N support

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

Updated setup.py version

fix bug where custom_parameters field is empty

PHX-255 Launch LTI provider on modal window open

PHX-241 Make modal display responsive

TNL-4046 Fix due date comparison bug

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

PHX-207 Accessibility Improvements

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'

Do not pin dependency versions

Sprint Solutions:Zug PHX-200 PHX-201 XBlock LTI Consumer