Reselect advanced schedule on modify task

[Richard Muvirimi]

When modifying an existing task with a schedule that's not one of the preset schedules, the app currently defaults to the Basic schedule. This can result in a different schedule being selected if the user doesn't notice the change. This was a noticeable issue when one wanted to just change a minor detail of the task such as the description or command but would then be required to select Advanced schedule or they would have to redo the scheduling part. With this pull request, the app will first check if the existing schedule is one of the preset schedules. If it is, that schedule will be selected by default. Otherwise, the app will default to the Advanced schedule.

I have made a pull request on GitHub addressing this.