Hide unpublished talks from schedule

Use the unpublish flag on presentations to hide them from the schedule
grid/mobile view as well as the schedule lists.
Show unpublished indicator for staff.

Adjust tracks on mobile schedule

Only display track if slot is not exclusive. Always use the first room
assisgned to the slot to determine the track name.

Update mobile schedule

Display track details on talks if available.
Show day end time slot as per desktop view.

Fix schedule edit

Use main base template instead of intermediate base.
Remove references to Bootstrap 3 and update to Bootstrap 4.
Add edit button to standard grid/mobile view instead of duplicating.

Styling for schedule

Update to Bootstrap 4 throughout.
Remove unused blocks and elements from past conferences.
Ensure schedule works in print mode.