* FIX: Better server-side check for appointment time availability;
* FIX: Attach Add Slot event to slots wrapper context to avoid unexpected behaviour;
* FIX: Calendar arrows direction in RTL;
* FIX: Show loader while getting new providers;
* FIX: Form error when using time range with only start time;
* FIX: Prevent PHP errors in some cases;
* FIX: Click on capacity doesn't select slot.
