Assign moderators to sessions individually

We have renamed the two session cancel options to better reflect their functionality.

• Cancel and remove user: Cancels the sessions and removes the participant from the project. They won't be able to schedule another slot.
• Cancel and ask for a reschedule: Cancels the session while giving the tester the option to choose another slot from the available times.

Fixed an issue with longer transcriptions failing to load in time. Transcriptions should now process in about 5-15 minutes depending on session length.