Scheduler does not update tasks on backend

[Minusome]

Bug Summary:

From JSDoc in TaskScheduler: "The existing tasks may have their schedules modified"

However, in the addTask method it doesn't seem that displaced tasks are updated on the server.

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Steps To Reproduce

Not reproducible until #274 closed. Once that issue is closed reproduce by:

1. Add a new task
2. Add another task with an earlier deadline that should occur before the first task (causing the first task to be moved)

Expected behaviour

First task startdate, enddate, reminderdate details updated on server.

Observed Behaviour

First task not updated on server.

Environment

• Version: All
• Operating System: macOS
• Browser (if any): Chrome

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[Minusome]

Blocked by #274