Handle conflicting appointments

[agentphoenix]

Overview

Update the availability and booking engines to handle conflicts.

Requirements

• For recurring services, check each date and if there is a conflict, give the user credit for that date and don't book the event.
• In the event that more than 50% of the instances have conflicts, do not allow the user to book and notify them there are too many conflicts.

Requires #24 to be completed first.

Estimate

20 hours