If the event/shift that a location/role was referencing had been marked
for deletion the sanity check would incorrectly refuse to delete the
event/role. Fix by ignoring deleted events/shifts.
Add utility methods to more easily edit the fields of a single entity in
the schedule, along with a modification flag and is modified utility to
check for changes having been made.
The Vue Ref system and assiated proxies does not work with the native
EcmaScript private fields, replace them with the TypeScript access
modifiers which are regular fields under the hood.
Write the logic of keeping track of location modifications and applying
updates from the server into the ClientSchedule class. This should
serve as the foundation for replacing the prototype in-component update
logic which have turned into an unmaintainable spagetti.
