Replace the convoluted useAccountSession composable with a pinia store
that in addition allows for the consolidation of all session related
functions to grouped into one module.
Render the timeslots as an editable table of times with associated
event. When the event it's linked to is edited the time slot is removed
from the original event it belonged to and added to the possibly new
event it now belongs to. This gives a somewhat intutive editing
experience when editing time slots linked to events with multiple times.
