Add recognition to time slot

This might be asking too much:

When quickly adding a time slot + client in a location where a similar time slot already exists (e.g., booking a PT session next to a block that already contains PT sessions), the system could perhaps recognize this and simply add the booking to the existing session block instead of creating a new block next to it.

Of course, we can easily work around this visual issue ourselves by using the new slider to display only the booked sessions.